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cond-mat.mtrl-sci

Materials Science

Techniques, synthesis, characterization, structure. Structural phase transitions, mechanical properties, phonons. Defects, adsorbates, interfaces

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cond-mat.mtrl-sci 2026-05-13 Recognition

Machine learning automates phase identification in powder diffraction

Automated multiphase identification and refinement in powder diffraction using mismatch-tolerant machine learning

RADAR-PD generates hypotheses from elemental constraints and refines them recursively for both X-ray and neutron data.

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Powder diffraction is a primary structural characterization tool in materials science, yet automated phase identification remains a major bottleneck for autonomous discovery. Existing workflows rely heavily on search--match heuristics and manual Rietveld refinement, and broadly usable end-to-end automation is especially limited for neutron powder diffraction, where comparable tools are largely absent. Here we introduce RADAR-PD, a modality-aware machine learning framework for phase identification and quantification across both X-ray and neutron powder diffraction. RADAR-PD couples a mismatch-tolerant neural network operating on coarse momentum-transfer fingerprints with automated lattice nudging and physics-constrained Rietveld verification, enabling dominant-phase hypotheses to be generated from elemental constraints and secondary phases to be isolated recursively. On an experimental RRUFF PXRD benchmark, RADAR-PD outperforms DARA in recovering the reference phase. RADAR-PD further provides robust multiphase analysis on complex time-of-flight and constant-wavelength neutron datasets, addressing an important unmet need in automated neutron diffraction analysis. These results establish RADAR-PD as an auditable, instrument-agnostic framework for autonomous structural discovery.
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cond-mat.mtrl-sci 2026-05-13 Recognition

Equivariant framework builds n-dependent Hamiltonians for magnets

Equivariant Space Group and Hamiltonian for Collinear Magnetic Systems

Symmetry construction for collinear systems enables topological pumping studies and ab-initio modeling of orientation effects

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Condensed matter physics increasingly focuses on exploiting the magnetic order parameter orientation n as a tuning knob for properties of collinear magnetic materials, but a general method for constructing effective Hamiltonians with explicit n-dependence has been lacking. Here, we develop a symmetry-based framework, built on the equivariant space group, for constructing such Hamiltonians, termed equivariant magnetic Hamiltonians (EMHs). The resulting EMH lives in a higher-dimensional k-n space and exhibits unconventional symmetry actions and topological features. Using a 1D ferromagnetic chain and a 3D antiferromagnet as examples, we demonstrate that explicit n-dependence in EMHs enables the study of magnetic-dynamics-driven topological pumping, including even-integer charge pumping and a second-Chern-number-induced quantized pumping of surface anomalous Hall conductivity. Beyond model systems, we incorporate the framework into first-principles calculations to construct ab-initio EMHs that accurately capture the n-dependent band structures of real materials. The approach can also be generalized to non-collinear magnetic systems. Our work establishes a general framework for constructing EMHs and for exploring the rich physics arising from magnetic anisotropy and magnetic dynamics.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

Fixed electronic shape plus recoil kernel fits graphene spectra to 8 keV

Graphene lattice recoil in hard X-ray photoemission: Experiment and Theory

Convolution of low-energy intrinsic response with photon-energy-dependent phonon kernel reproduces line shapes and centroid shifts without a

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Hard-x-ray C 1s photoemission from monolayer graphene probes a regime in which nuclear recoil and intrinsic electronic asymmetry contribute on comparable energy scales to the observed spectral line shape. Here we combine experiment and modeling over the photon-energy range 0.8 keV--8 keV to resolve this interplay quantitatively. A graphene-specific implementation of the Fujikawa--Takata cumulant formalism, based on an anisotropic vibrational density of states constrained by first-principles phonon calculations, captures the expected recoil scaling with photon energy and emission geometry but fails to reproduce the pronounced asymmetric tails of the measured spectra. To overcome this limitation, we introduce an explicit electronic convolution model in which an intrinsic, photon-energy-independent electronic line shape extracted from near-recoilless 0.8 keV data is convolved with a phonon recoil kernel carrying the full dependence on photon energy and emission angle. This approach reproduces both the measured line-shape evolution and the observed centroid shifts across the explored energy range without refitting the spectra at higher photon energies. The results show that recoil in graphene cannot be described by a baseline treatment in which the phonon recoil kernel is combined only with symmetric lifetime broadening, but must be treated together with the intrinsic many-body electronic response of the C 1s line.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

Ordering sets magnetism in FePt Janus particles

Ordering governs magnetic tunability in FePt-based Janus particles independent of curvature

Coercivity holds steady across 3-10 micrometer sizes while ordering changes alter reversal, giving a clear size boundary for geometry-driven

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Magnetic Janus particles enable remote actuation in biomedical, microfluidic, and materials applications. While curvature-driven magnetic effects are well known at the nanoscale, their influence on magnetization reversal in micrometer-sized particles is still unclear. In this work, we combine experiments and micromagnetic simulations to study curvature-dependent magnetism in FePt-coated Janus particles with diameters ranging from 3-10 microm, and extend the analysis to 1-20 microm through simulations. Structural and crystallographic characterization confirms continuous FePt coatings with near-equiatomic composition and partial L1_0 ordering. Magnetometry measurements show nearly unchanged hysteresis behavior across particle sizes, with coercivity remaining approximately constant m_0Hc = 1.13 +/- 0.05 T, pooled n = 8). Statistical analysis reveals no significant dependence of coercivity or remanence on particle diameter (p = 0.61 for Hc and p = 0.85 for Mr/Ms). To explain these results, we introduce FunMaP, an open-source micromagnetic simulation framework that enables direct comparison between experiments and idealized FePt caps. Simulations confirm that curvature has little effect on magnetization reversal at micrometer scales, consistent with a locally planar magnetic limit where the exchange length is much smaller than the particle radius. In contrast, differences in chemical ordering strongly affect hysteresis shape and coercivity. These findings demonstrate that magnetic behavior in micrometer-scale FePt Janus particles is governed mainly by material ordering rather than curvature. This work establishes a quantitative boundary for curvature-dependent magnetism and provides design guidelines for programmable magnetic micro-systems.
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cond-mat.mtrl-sci 2026-05-13 Recognition

S-doping shifts few-layer graphene from linear to flat bands

Engineering few-layer graphene by S-doping: from sustaining linear dispersion to flat bands

Specific sulfur placements in one to four layers open gaps or flatten bands near the Fermi level, allowing tuning between metallic and flat,

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Motivated by the technological relevance of S-doped few-layer graphene (FLG) in battery applications and in the oxygen reduction reaction, we systematically explore the effect of basal plane S-doping on the electronic properties of mono-, bi-, and four-layer graphene, using first-principles calculations with van der Waals corrections. In the monolayer we find a variety of effects ranging from a sustained Dirac cone with localized impurity bands away from the Fermi level in thiophenic doping (2V1S) to a band gap opening of 0.4 eV and flat bands close to the Fermi-level in graphitic doping (1V1S) and an additional $n$-type doping together with spin-polarization, when three S-atoms are adsorbed in a four-site vacancy (4V3S). Incorporation in FLG leads to modification of the Dirac cone into a set of hyperbolic touching bands in 2V1S; reduction (bilayer) and closing of the band gap with additional hyperbolic touching bands in conjunction with the flat band at the Fermi level in 1V1S and 4V3S and a reduction of spin polarization in the latter. Overall, S-doping enables design of the band structure and tuning the electronic behavior of FLG from metallic to insulating and from linear dispersive to flat bands that makes S-doped FLG a promising material for versatile technological applications.
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cond-mat.mtrl-sci 2026-05-13 1 theorem

Machine learning turns XPCS data into grain boundary kinetics

Probing Non-Equilibrium Grain Boundary Dynamics with XPCS and Domain-Adaptive Machine Learning

Domain-adaptive models trained on simulations extract diffusivity, stiffness and concentration from experimental fluctuation maps.

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Grain-boundary (GB) dynamics control the stability, mechanical, and functional response of nanocrystalline materials, but direct experimental access to their slow non-equilibrium motion has been limited. Here we establish X-ray photon correlation spectroscopy (XPCS), combined with domain-adaptive machine learning, as a quantitative probe of GB dynamics. Temperature- and grain-size-dependent two-time XPCS measurements in nanocrystalline silicon reveal pronounced departures from time-translation invariance, showing that GB relaxation can remain far from equilibrium over experimental timescales. However, direct extraction of quantitative physical information from these high-dimensional, noisy fluctuation maps faces a significant challenge. To overcome this barrier, we develop a semi-supervised learning framework that transfers physical parameter labels from continuum simulations to unlabeled experimental XPCS maps through domain-adaptive representation alignment. This AI-augmented approach enables the extraction of key kinetic parameters, including bulk diffusivity, GB stiffness, and effective GB concentration, directly from experimental XPCS measurements. Our results show how machine learning can transform indirect fluctuation signals into quantitative materials dynamics, providing a general route to study non-equilibrium defect motion in solids.
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cond-mat.mtrl-sci 2026-05-13 Recognition

Thermal history tunes cold crystallization energy in 10OS5

Competing crystallization pathways and cold crystallization kinetics in 10OS5 liquid crystal

Different cooling rates create glass or metastable crystals that release varying heat on reheating for potential storage use.

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The liquid crystalline 4-pentylphenyl-4'-decyloxythiobenzoate is investigated in various temperature programs for determination of crystallization kinetics and glassforming properties. The Avrami model, Augis-Bennett method and isoconversional method are used. Cooling at the 25-30 K/min rate results in formation of the glass of the tilted smectic Y phase with the herring-bone order within layers. Slower cooling leads to the partial or total (2 K/min) crystallization of the metastable Cr2 phase, which during subsequent heating or annealing in a proper temperature transforms to another Cr1 phase. Heating from the vitrified smectic Y leads to cold crystallization of the pure Cr1 phase or the Cr1/Cr2 mix. Both Cr1 and Cr2 are conformationally disordered crystal phases, which is indicated both by the melting entropy values and the dielectric spectra. The results demonstrate that the energy released during cold crystallization can be tuned by thermal history, highlighting 10OS5 as a candidate for thermal energy storage applications.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

AFM dissipation detects sub-band mobilities in SrTiO3 2DEG

Mechanical detection of sub-band mobilities of two-dimensional electron gas on reduced SrTiO₃(001) surface

Peaks tied to quantum capacitance follow Kohler's rule under magnetic fields to yield per-sub-band mobilities

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The two-dimensional electron gas (2DEG) in reduced strontium titanate offers a versatile platform for oxide electronics, yet its dissipation mechanisms under field driven charge fluctuations remain poorly understood. Here, we combine low-temperature atomic force microscopy with scanning tunnelling spectroscopy to probe the force and dissipation responses of a mechanical oscillator interacting with the STO 2DEG. The observation of Rydberg like image potential states by tunnelling experiments confirm the 2DEG formation, while dissipation spectroscopy reveals bias-dependent peaks linked to local electrostatic gating and charge redistribution within the 2DEG energy sub-bands. These features are quantitatively explained by variations in quantum capacitance as carrier density is tuned by electric fields. Under magnetic fields, dissipation peaks obey the Kohler's rule, allowing extraction of carrier mobilities in each sub-band. Our results establish a non-invasive AFM - based methodology for quantifying energy losses in quantum oxides, providing new insights into charge dynamics relevant for spintronic applications.
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cond-mat.mtrl-sci 2026-05-13 1 theorem

Alternating layers raise impact energy dissipation by over 50%

Enhanced Impact Mitigation via 3D-Multilayered Material Architectures

Mass-matched monolithic and octet lattice stacks outperform uniform architectures by localizing failure and controlling wave propagation in

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Materials designed by nature commonly exhibit functional grading and laminated structures, particularly when intended for enhanced impact protection. Synthetic materials have also found success in exploiting this concept with fully dense but spatially varying architectures, as is the case with advanced fiber-based composites. In the lightweight materials space, porous architected materials have shown benefits for extreme impact mitigation, proving to be advantageous in dissipating large amounts of energy per unit mass, but rarely harness the benefits of layering or functional grading in designs. Here, a design paradigm for lightweight multilayered materials towards high impact-mitigation efficacy is demonstrated, showing that the use of alternating monolithic and beam-based architectures leads to enhanced and predictable responses under extreme conditions. These layered, mass-equivalent `heterostructures' with different ordering and proportions of octet and monolithic layers outperform single-architecture lattices on a mass-normalized energy dissipation basis by >50% when subjected to supersonic microparticle impact. Through analysis that combines wave-propagation analysis, nonlinear finite element simulations, and post-impact crater reconstruction, layer-by-layer mechanical properties are mapped to crater formation and energy dissipation behaviors. This heterostructure design framework offers a simple approach towards tuning failure and impact resistance of materials for protective applications from Whipple shields to sports equipment.
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cond-mat.mtrl-sci 2026-05-13 Recognition

Two quantum materials deliver 4-volt magnesium cathodes

Discovery of High-Voltage Magnesium-Ion Cathodes using Machine Learning and First-Principles Calculations

Screening 917 topological candidates with a neural network and DFT yields stable materials at 3.66 V and 4.06 V average voltage.

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Developing high-performance cathode materials for magnesium-ion batteries (MIBs) remains challenging because Mg$^{2+}$ ions move slowly, and conventional materials exhibit low voltage outputs. In this study, machine learning and first-principles calculations were combined to investigate topological quantum materials (TQMs) as a new class of cathode candidates. A modified crystal graph convolutional neural network (mCGCNN) was used to screen 917 Mg-containing TQMs, identifying a small subset of materials with predicted voltages above 3 V and high volumetric capacities. Among these, Mg$_2$VO$_4$ and Mg$_6$MnO$_8$ were selected for detailed density functional theory (DFT) analysis. Formation energy and convex-hull calculations indicate that Mg$_x$VO$_4$ exhibits a fully stable magnesiation pathway, whereas Mg$_x$MnO$_8$ demonstrates minor metastability at intermediate compositions. The calculated voltage profiles yield average voltages of 3.66 V for Mg$_2$VO$_4$ and 4.06 V for Mg$_6$MnO$_8$, in good agreement with machine learning predictions. Electronic structure analysis, supported by Wannier interpolation, confirms that both materials are semiconducting, with valence bands dominated by O $2p$ states and conduction bands by transition-metal $d$ states, indicating a charge-transfer redox mechanism. Compared to conventional Mg cathodes, these TQMs exhibit higher voltages and competitive capacities, underscoring their potential for next-generation multivalent batteries. This study demonstrates that integrating machine learning with first-principles calculations offers an efficient approach for discovering and understanding novel cathode materials.
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cond-mat.mtrl-sci 2026-05-13 Recognition

Vacancies stabilize N-N complexes that trap carriers deep in Ga2O3 gap

Vacancy-Enhanced N-N Bonding and Deep Level Complex Defect Formation in β-Ga₂O₃

DFT results show these stable defects introduce localized states from N and O p-orbitals, limiting transport and favoring semi-insulating Ga

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The formation and electronic properties of nitrogen-related defect complexes in $\beta-Ga_2O_3$ are investigated using first-principles calculations. Starting from the energetically favorable $N_{i9}-N_{OI}$ configuration, nitrogen atoms exhibit a strong tendency toward co-localization, leading to reduced $N-N$ separation. However, analysis of bond lengths and electron localization function shows that these configurations do not fully attain molecular $N_{2}$ character. The role of intrinsic defects is further examined by introducing oxygen and gallium vacancies. Vacancy-assisted configurations enhance local lattice relaxation and further decrease the $N-N$ distance. Formation energy calculations indicate that several vacancy-assisted complexes are thermodynamically favorable, while binding energy analysis confirms their stability against dissociation. Despite this, the density of states analysis reveals that all configurations introduce localized electronic states within the band gap. These states originate primarily from hybridized $N$-$2p$ and $O$-$2p$ orbitals and remain energetically separated from the band edges. Spin density analysis further confirms strong localization. Overall, these defect complexes act as deep trapping centers, limiting carrier transport in $\beta-Ga_2O_3$ and thereby promoting semi-insulating behavior and current blocking characteristics.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

Simulations map rod geometry and grain tilt to higher Alnico coercivity

Tailoring the material properties, nanostructure and grain alignment of Alnico magnets through micromagnetic simulations

Finite-element runs on exchange-decoupled rods plus a trained regressor reveal concrete trends for improving rare-earth-free magnets.

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Alnico magnets have gained renewed interest in the search for rare-earth free permanent magnets due to their high thermal stability and magnetisation. However, the limited coercivity of these shape-anisotropy-based alloys constrains their performance. Starting from a reference Alnico sample, we realised a finite elements micromagnetic study of exchange-decoupled rods by varying their dimensions and interrod spacing across those observed experimentally. We computed the hysteresis properties by progressing from micromagnetic simulations of a small number of rods within the magnetostatic field of their neighbours to large systems treated statistically based on the distribution of orientations of the grains. We compared the coercivity of an isolated rod with that of the exchange-decoupled system to highlight the effect of magnetostatic interactions. We computed analytically the stray field acting on a single rod as a consequence of its surrounding rods in order to confirm the scaling of the coercivity with the packing fraction p. We explored how intrinsic material properties influence magnetic behaviour by examining materials with different magnetocrystalline anisotropy constants and saturation polarisation values. Results from several hundred simulations were used to train a multi-layer perceptron regressor and predict the magnetic properties as function of the dimensions of the rods, interrod spacing and orientation of the grains. With this approach, we highlight the underlying trends by which nanoscale structuring, intrinsic material properties and grain alignment can be tailored to improve the magnetic properties of Alnico alloys.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

Fe3Sn2 susceptibility isotherms collapse at isosbestic points

Universality of magnetic susceptibility in the conical state of kagome ferromagnet Fe₃Sn₂

DMS data reveal quadratic temperature corrections and stripe-to-bubble domain evolution in the conical state near 0.6 T

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We report universal behavior of the differential magnetic susceptibility (DMS) in the conical phase that mediates the spin-reorientation (SR) transition of the kagome ferromagnet Fe$_3$Sn$_2$. Within the SR temperature range, the DMS isotherms exhibit extremely narrow crossing regions, forming isosbestic points. Using an isosbestic-invariance analysis, we show that the isotherms collapse onto a single temperature-independent curve, revealing quadratic-in-temperature corrections to the susceptibility. Complementary field-dependent magnetic-force-microscopy measurements uncover evolution of spin textures from stripe-like domains at low fields to isolated bubble-like domains near the isosbestic field ($\sim 0.6$~T), a behavior not previously reported in bulk Fe$_3$Sn$_2$ within the conical state. These findings point to a universal mechanism for the emergence of complex magnetic textures near isosbestic points, driven by the competition between magnetocrystalline anisotropy, dipolar interactions, and external magnetic field.
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cond-mat.mtrl-sci 2026-05-13 Recognition

Ti-based glass sets new specific strength record at 13% strain

Synergistic improvement of specific strength and plasticity achieved in Ti-based metallic glass designed based on quasicrystal structure

Al microalloying inherits quasicrystal short-range order to break the strength-plasticity trade-off

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Achieving a balance between low density, high strength, and good ductility remains a major challenge in the development of structural materials. Ti-based bulk metallic glasses (BMGs) have attracted considerable attention due to their exceptionally high specific strength. However, the intrinsic strength-plasticity trade-off has hindered their practical applications. Based on a quasicrystal-derived structural heredity and minor-element microalloying, this work realizes a synergistic enhancement of specific strength and plasticity in Ti-based BMGs. The resulting ((Ti_{40}Zr_{40}Ni_{20})_{72}Be_{28})_{97}Al_{3} BMGs demonstrate an ultrahigh specific strength of 5.34 \times 10^5 \text{ N}\cdot\text{m}\cdot\text{kg}^{-1}, establishing a new record for Ti-based BMGs, along with a plastic strain of 13\%, breaking through the traditional strength-plasticity limitation of BMGs. Structural analyses show that Al microalloying effectively inherits and modulates the short-range order derived from quasicrystalline structures, thereby achieving an observed synergistic enhancement in both strength and plasticity. This work provides new insights into composition design and lightweight structural applications of Ti-based BMGs.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

Descriptors from theory identify new inorganic electrides

Theory and Discovery of Electrides

The framework explains why electrons localize in interstices and applies to high-pressure and organic cases as well.

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Electrides are materials with electrons localized at interstitial regions of the crystal lattice and have been identified as promising candidates for a variety of applications, including catalysis, electron emission, and superconductivity. We present a theoretical framework for the origin of interstitial electrons in electrides. We demonstrate that this theory can explain electride-like behavior in prototypical electrides, and we use it to develop descriptors for the high-throughput discovery of new inorganic electride candidates from first principles. We also show that the same concepts can explain electride-like behavior in other classes of material, including high-pressure electrides and organic electrides and, more broadly, provide an alternative understanding of F-center defects and solvated electrons.
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cond-mat.mtrl-sci 2026-05-13 Recognition

ML surrogates cut lattice thermal conductivity prediction costs by orders of magnitude

Fast and Accurate Prediction of Lattice Thermal Conductivity via Machine Learning Surrogates

Benchmarks show MLIP models excel inside known ranges while deep networks like ALiEGNN handle unseen low-conductivity materials better.

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The appearance of generative models has opened vast chemical spaces in the design of functional materials. Although machine learning interatomic potentials (MLIPs) have substantially accelerated phonon calculations, high-fidelity prediction of lattice thermal conductivity \k{appa}lat still requires accurate treatment of anharmonic interactions, which remains a key challenge for existing potentials across novel chemical spaces. To address this challenge, we present a comprehensive benchmark of 15 surrogate models for predicting \k{appa}lat using the Phonix database, which contains 6,966 entries with anharmonic phonon properties derived from first-principles calculations. Firstly, We categorize these surrogate models into three distinct groups: Physical-informed feature descriptors combined with ML models, end-to-end deep neural networks, and pre-trained MLIP-embeddings combined with ML models. By evaluating model performance across random, space-group disjoint (testing generalization to unseen crystal symmetries), and Out-Of-Distribution splits (OOD dataset that testing extrapolation to property regimes beyond the training range) based on \k{appa}lat, we probe both interpolation and exploration capabilities. Our results reveal that MLIP-embedded models excel in interpolation within well-sampled regions, deep neural network models especially ALiEGNN demonstrate superior robustness in OOD regimes critical for discovering novel low-\k{appa}lat. Additionally, we find a systematic degradation in performance when the structural representation is reduced. Although surrogate models exhibit lower accuracy than direct simulations using first-principles calculation, they reduce computational costs by orders of magnitude, enabling efficient high-throughput screening of thermoelectric materials with minimal loss in generative design workflows.
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cond-mat.mtrl-sci 2026-05-13 2 theorems

G0W0 in numerical atomic orbitals matches plane-wave accuracy

G⁰W⁰ implementation based on the pseudopotential and numerical-atomic-orbital basis-set framework: Algorithms and benchmarks

A compressed resolution-of-identity scheme and analytic small-q treatment enable efficient large-system simulations with established code

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The $GW$ method delivers substantially improved accuracy in electronic band structure calculations over conventional Kohn-Sham density functional theory (KS-DFT) by explicitly incorporating the electron self-energy effect beyond mean-field approximations. Despite many existing implementations, a periodic $GW$ implementation within the framework of numerical atomic orbitals (NAO) combined with the pseudopotential (PP) scheme has not been reported. This is urgently needed given the increasing popularity of the NAO-PP framework in KS-DFT calculations and its importance for the development of machine-learning electronic-structure approaches. In this work, we present an efficient NAO-PP-based $G^0W^0$ computational framework by interfacing the first-principles software package ABACUS with LibRPA -- a library for performing low-scaling random-phase approximation and $GW$ calculations based on NAOs. Our approach employs the localized resolution of identity (LRI) technique with a novel compression scheme, significantly improving both computational efficiency and numerical stability. In addition, an analytic treatment of the small-q limit of the microscopic dielectric function reduces the need for dense q-point sampling. Furthermore, we propose a practical strategy to select a suitable KS-DFT pseudopotential prior to $G^0W^0$ calculations by examining the frequency-dependent macroscopic dielectric function. Systematic benchmarks validate the effectiveness of our compression scheme and real-space tensor filtering strategies, demonstrating both high accuracy and significant computational efficiency gains. Comparisons with established $G^0W^0$ implementations show excellent agreement in band structures and band gaps, confirming ABACUS+LibRPA as a reliable and efficient platform for large-scale $G^0W^0$ simulations.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Periodic defects open band gap in graphene only for multiples of three

Symmetry Guided Band-Gap Opening via Periodic Topological Defects in Graphene

Zone folding merges Dirac points when supercell size N is a multiple of three, producing larger tunable gaps with flower defects.

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Graphene lacks an intrinsic band-gap, which limits its use in electronic applications. Here we demonstrate that periodic arrays of topological defects can open and control a band-gap in a predictable manner governed by defect spacing and lattice symmetry. Using first-principles density functional theory calculations supported by tight-binding models, we investigate graphene superlattices containing Stone-Wales and flower-like defects over a range of $N \times N$ periodicities, where $N$ determines the defect separation. We show that band-gap opening occurs only when translation symmetry is reduced in a specific way: for supercells with $N$ a multiple of three, Brillouin-zone folding brings the Dirac cones at $K$ and $K'$ to the same momentum in the reduced Brillouin zone. In particular, flower-like defect superlattices produce larger and tunable band-gaps, whose magnitude decreases systematically with increasing defect separation and approaches zero in the dilute-defect limit. These results establish a predictive framework for band-gap engineering in defect-patterned graphene and clarify the microscopic mechanism underlying gap formation in periodically reconstructed lattices.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Dual doping yields 11 GPa hardness in nanocrystalline nickel

Synergistic doping of the grain interior and grain boundary alters deformation mechanisms and enables extreme strength in nanocrystalline Ni-Cr-Y alloys

Cr inside grains and Y at boundaries suppress sliding and rotation while grain size stays fixed.

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Solid solution addition and grain boundary segregation have been independently shown to enhance the strength of nanocrystalline alloys. In the present study, the synergy between these two effects is investigated in nanocrystalline Ni-Cr-Y sputtered films through systematic variation of alloying element contents with grain size kept constant. Cr is introduced into a solid solution and serves to strengthen the lattice, while Y segregates to the grain boundaries to stabilize these features. Nanoindentation is used to probe hardness, with unexpected trends and very high values observed. Cr additions led to nanocrystalline solid solution strengthening, yet saturation was observed at higher concentrations due to the emergence of grain boundary dominated processes, as evidenced by pile-up morphologies containing slip steps and grain rotation. Y segregated to the grain boundaries, enhancing boundary-mediated strengthening by pinning the dislocations and suppressing dislocation emission, grain boundary sliding, and grain rotation processes. With increasing Y concentration, the nanocrystalline solid solution strengthening effect induced by Cr addition becomes weaker. This phenomenon can be attributed to a reduced dislocation bowing distance caused by dopant pinning. Most notably, the strongest ternary Ni-Cr-Y alloy exhibited a hardness of 11.0 GPa, among the highest hardness values reported for single-phase Ni-based alloys. These findings highlight how tuning grain and grain boundary chemistry offers a viable strategy to control dislocation mechanics and improve the strength of nanocrystalline metals.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

NA effects alter dielectric screening in pentacene crystal

Application of the exact-factorization density-functional perturbation approach to pentacene crystal and monolayer MoS2

But they prove negligible in stiff MoS2 monolayer, highlighting material dependence from soft modes and electron-phonon coupling.

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Non-adiabatic effects arising from electron-phonon interactions are often neglected within the Born-Oppenheimer (BO) approximation, which assumes that electronic states adjust instantaneously to nuclear motion. The exact factorization (EF) formalism provides a rigorous framework for treating such effects beyond the adiabatic regime and has recently been adapted to density functional theory (DFT) in the harmonic limit. Building on these foundations, we previously introduced an EF-based perturbative scheme, the EF density-functional perturbation theory (EF-DFPT), that enables the computation of phonon-driven non-adiabatic (NA) corrections to Kohn-Sham (KS) electronic states, up to second order in nuclear displacements. Here, we present the first implementation and application of EF-DFPT to extended periodic materials, focusing on its impact on experimentally relevant observables. Using the pentacene molecular crystal and monolayer MoS2 as representative soft- and stiff-mode systems, respectively, we demonstrate how NA electron-phonon interactions modify the static dielectric response. We show that these modifications originate from the combined effect of NA phonon-dressed electronic wavefunctions and second-order NA energy renormalizations. The resulting behavior is strongly material dependent: NA effects are negligible in monolayer MoS2, whereas in pentacene they lead to pronounced long-range screening effects associated with soft vibrational modes and enhanced electron-phonon coupling.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Parity forbids optical transition in 4H-Ge

Optical selection rules in hexagonal Ge polytypes and their lifting by symmetry perturbation

Single silicon substitutions break symmetry and shorten radiative lifetimes by orders of magnitude in hexagonal germanium polytypes.

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Hexagonal germanium polytypes have emerged as promising direct-gap semiconductors for silicon-integrated optoelectronics, yet their optical properties remain largely unexplored beyond the well-studied 2H phase. We present a comprehensive theoretical study of optical properties of hexagonal 2H-, 4H-, and 6H-Ge polytypes through ab initio calculations of quasiparticle band structures, dipole transition matrix elements, and solution of the Bethe-Salpeter equation. While all three polytypes exhibit direct band gaps of increasing size from 2H to 6H, we reveal that the fundamental optical transition in 4H-Ge is parity-forbidden due to matching band parities at the valence and conduction band edges. This selection rule results in a radiative lifetime seven orders of magnitude longer than in 2H- and 6H-Ge, severely limiting light emission capabilities. To demonstrate that the selection rule can be lifted, we introduce controlled symmetry perturbations by substituting single Ge atoms with Si in each unit cell, breaking the crystal symmetry. This perturbation increases the optical matrix elements by up to two orders of magnitude and reduces radiative lifetimes for all perturbed polytypes. We also compute absorption coefficients and frequency-dependent dielectric tensors for both light polarizations, including excitonic effects up to 5 eV, providing complete optical characterization of ideal and symmetry-perturbed hexagonal Ge systems relevant for optoelectronic applications.
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cond-mat.mtrl-sci 2026-05-12 Recognition

Adamantane films flip triboelectric sign via plasma orientation

Adamantane plasma polymers: fluorine-free vacuum-processable triboelectric thin films for all-triboelectric nanogenerator configurations

Facing or backfacing deposition creates positive and negative layers for versatile nanogenerator designs

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Triboelectric nanogenerators (TENGs) are major drivers in on-site power generation for smart devices, enable self-powered sensors, and introduce novel catalytic processes. Here, we present the advantages of adamantane plasma layers as bivalently triboelectric surfaces capable of exhibiting both tribopositive and tribonegative character through simple modification of the synthesis conditions without the need for additives or functionalization. Fabrication facing or backfacing the plasma yields thin film polymers with different dielectric constants, Young's moduli, and secondary electron emission. The conformality, stability, and processability of the polymers enable direct implementation across solid-solid, solid-liquid, and hybrid piezo-triboelectric configurations. Additional texturization by buckling is shown to provide voltage and current outputs as high as 90 V cm2 and 0.6 uA for a 2.8 um (tribonegative) vs. 400 nm (tribopositive) combination. A maximum power density of 2.1 uW cm-2 is generated from salty droplets in a switch-electrode drop-TENG configuration employing a 500 nm-thick tribopositive adamantane polymer as the triboelectric surface. These layers have demonstrated outstanding durability, enabling more than 10^5 cycles in solid-solid nanogenerators and 10^4 droplet impacts in solid-liquid configurations. The synthetic method is environmentally friendly and industrially scalable, making the adamantane plasma polymer a reliable and competitive solution for thin film triboelectric materials.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Spectrum match confirms Eu-N9 plane model in SiAlON phosphor

Micro-environment of the Eu interstitial in β-SiAlON:Eu²⁺ green phosphor

Reproducing 6 K vibronic peaks at low z validates nine-nitrogen coordination and explains why phonon replicas persist while emission red-sh

Figure from the paper full image
abstract click to expand
The precise atomic-scale structure around Eu$^{2+}$ activators in the $\beta$-Si$_{6-z}$Al$_z$O$_z$N$_{8-z}$:Eu$^{2+}$ commercial green phosphor remains elusive. We use the first-principles $\Delta$SCF excited-state method, embedding of the interatomic force constants for supercells up to 3501 atoms, and Huang-Rhys theory to clarify this issue. Monte Carlo exploration is used to identify representative low-energy structural models spanning different levels of Al/O concentration $z$. For the lowest-energy structure at low $z$, our computed photoluminescence spectrum reproduces the experimental vibronic peaks at 6~K with excellent agreement in peak positions and intensities, validating the Eu-N$_9$ coordination model with Al, O, and Eu confined to the same crystallographic plane. Analysis of the low-energy structures reveals that the electron-phonon coupling is weak ($S \approx 2.15$) with a robust characteristic phonon signature across different Al/O arrangements, explaining the surprising persistence of resolved phonon replicas with increasing $z$. We explain the experimentally observed red-shift of emission with increasing $z$ through systematic trends in zero-phonon line energies, modest increases in Huang-Rhys factors, and larger configurational diversity at higher compositions.
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cond-mat.mtrl-sci 2026-05-12 Recognition

Equilibrium vacancy concentration fixes screening reference for CaMnO3

Oxygen vacancies beyond the dilute limit in doped CaMnO3 perovskites and implications for screening materials in thermochemical applications

OVFE curves referenced to this minimum match experimental reduction enthalpies and distinguish A-site versus B-site doping mechanisms.

Figure from the paper full image
abstract click to expand
Thermochemical energy storage (TCES) in oxide perovskites relies on reversible oxygen vacancy formation, and computational high-throughput screening of candidate materials has predominantly used the single oxygen vacancy formation energy (OVFE) as the key descriptor. We demonstrate that the OVFE is insufficient for screening cubic CaMnO3 perovskites, because the stoichiometric compound is not the minimum energy reference state; vacancies are inherently present at operating temperatures. Materials with negative single OVFEs are routinely excluded from screening datasets as unsuitable, but this reflects a mischoice of reference state rather than a genuine materials limitation, and risks discarding promising TCES candidates. We address this by computing OVFEs as a function of vacancy concentration using ab initio density functional theory, establishing the equilibrium vacancy concentration as the correct reference point. OVFE curves referenced to this minimum align with experimentally measured reduction enthalpies, providing a framework directly comparable to experiments. We further show that A-site and B-site doping modify the vacancy formation landscape through distinct mechanisms. A-site dopants act primarily through strain relaxation and symmetry breaking, while B-site dopants reshape the local redox environment and introduce strong configurational dependence. Finally, we develop a thermodynamic model incorporating configurational entropy that accurately predicts equilibrium oxygen stoichiometry as a function of temperature and oxygen partial pressure and reveals that selective reduction of Mn4+ versus B-site dopant ions can tune the onset temperature for vacancy formation. These results establish a screening framework for perovskite TCES materials and provide practical guidance for extending high-throughput workflows beyond the single-vacancy paradigm.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

One parameter controls thermodynamics and dynamics of dislocation loops

Thermodynamics and dynamics of non-compact prismatic dislocation loops simulated using a machine-learning model

A universal measure of ground-state shape irregularity sets energy, entropy and diffusion for prismatic loops.

Figure from the paper full image
abstract click to expand
We explore how the thermodynamic properties and dynamics of a self-interstitial prismatic dislocation loop are affected by microscopic-scale variations in its geometric configuration, an aspect that rarely received attention in literature. First, we develop a machine-learning (ML) model to predict the formation energy of an arbitrary geometrically complex configuration of a self-interstitial atom dislocation loop. Trained on atomistic simulation data, the ML model achieves high predictive accuracy across a broad range of configurations, with a typical error in the 1% range. Second, from the ML model, we evaluate the density of configurational microstates as a function of loop's formation energy and derive analytical expressions valid in tractable limiting cases. Using statistical mechanics, we derive the configurational free energy, the average energy, and the thermodynamic entropy of a dislocation loop as a function of temperature. Third, we simulate the dynamics of self-climb of dislocation loops with various geometries and evaluate their diffusion coefficients and effective activation energies. Our analysis shows that there is a single universal parameter describing the morphological irregularity of loop configurations in its ground state. This parameter determines the thermodynamic properties of a loop as well as its dynamics, and simulations illustrate how the properties and mobility of a configurationally complex loop vary as functions of the irregularity parameter.
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cond-mat.mtrl-sci 2026-05-12 1 theorem

ML model predicts BCC phases in cobalt-free alloys at 84% accuracy

Data-driven body-centered cubic phase prediction in cobalt free high-entropy alloys

Six parameters plus augmented data identify mixing enthalpy and size difference as key drivers for nuclear-grade high-entropy alloys.

abstract click to expand
High-entropy alloys (HEAs) are known for superb combination of performance attributes, making them ideal for advanced applications, e.g., nuclear engineering. The concept of cobalt-free HEAs aims to mitigate concerns about cobalt's radioactivity, however, predicting their phase formation remains challenging due to their complex compositions. In this work, we integrate six semiempirical parameters, i.e., mixing entropy ({\Delta}Smix), mixing enthalpy ({\Delta}Hmix), atomic size difference ({\delta}), valence electron concentration (VEC), d-orbital energy level (Md), and the {\Omega} parameter, along with machine learning (ML) to predict the body-centered cubic phase stability in Co free HEAs. To address the limitations of experimental data, generative adversarial networks were used to augment the dataset, thus improving the accuracy of the Gaussian process classification model used for phase prediction. After dimensionality reduction to five principal components, the model achieved an accuracy of 84%, with {\Delta}Hmix and {\delta} identified as the key descriptors influencing phase formation. This approach highlights the synergy of ML and data augmentation in accelerating the design of HEAs for advanced applications.
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cond-mat.mtrl-sci 2026-05-12 Recognition

Giant Hall conductivity from Weyl points in RGaGe semimetals

Rare-Earth-Tuned Evolution from d- to f-Orbital Dominance and Giant Anomalous Hall Effect in Topological RGaGe (R = Ce, Pr, Nd) Semimetals

Rare-earth choice shifts orbital character from d to f while sustaining the topological anomalous Hall response above magnetic order.

Figure from the paper full image
abstract click to expand
The family of noncentrosymmetric rare-earth germanides RGaGe (R = Ce, Pr, Nd) provides a rich materials platform to explore the intertwined physics of strong magnetism, electronic correlations, and topological band structures. Through a combination of crystal growth, characterization, and first-principles calculations, we reveal that these compounds exhibit a pronounced uniaxial magnetic anisotropy, leading to distinct ground states: RGaGe orders ferromagnetically with moments along the crystallographic c-axis, and shows an antiferromagnetic-like structure in the ab-plane. A key finding is a significantly enhanced intrinsic anomalous Hall conductivity (AHC) compared to their well-known RAlGe counterparts, which even reaches as high as 948 {\Omega}-1 cm-1 at 2 K in PrGaGe. Our theoretical analysis predicts that this AHC originates from a robust Weyl semimetallic state driven by inversion symmetry breaking, where Weyl points near the Fermi level couple strongly to the magnetic order. Importantly, this topological state persists above the magnetic ordering temperature, confirming its intrinsic electronic origin. Our calculation also reveals that, while the near-Fermi-level states in CeGaGe and PrGaGe are dominated by d-orbital contributions, NdGaGe exhibits significant f-orbital involvement, signaling a progressive evolution from d- to f-orbital dominated topology. These results establish the RGaGe system as a tunable platform for systematically extending the RAlGe-related family, showcasing a large anomalous Hall response and orbital evolution near the Fermi level, and advancing the understanding of the interplay between topology and magnetism in quantum materials.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Two-step laser demagnetization reveals 2D magnetism in MAX phase

Laser-induced demagnetization in a MAX phase (Cr0.5Mn0.5)2GaC

The (Cr0.5Mn0.5)2GaC film shows a fluence-dependent fast stage and a dominant 100-ps stage whose spin heat capacity varies little with温度.

Figure from the paper full image
abstract click to expand
Magnetic MAX phases are nanolaminated metals that combine ceramic-like thermal and mechanical stability with peculiar magnetic ordering, making them attractive for thin-film optoelectronics and spintronics. However, their magnetization dynamics remain largely unexplored. Here, we investigate laser-induced ultrafast demagnetization in a 40-nm-thick epitaxial film of the magnetic MAX phase (Cr0.5Mn0.5)2GaC, which magnetically orders below ~250 K, using time-resolved magneto-optical Kerr effect spectroscopy. We reveal, that the demagnetization transients exhibit a two-step type-II demagnetization - a signature of two-dimensional magnetic systems. The fast demagnetization stage is small at low temperatures and fluences but becomes prominent with increasing excitation. The second stage dominates the process and has a characteristic time of approximately 100 ps. Applying the three-temperature model, we extract the electron-lattice, spin-lattice, and electron-spin coupling constants. The reconstructed spin heat capacity exhibits a weak temperature dependence, accounting for the absence of significant slowing down of demagnetization at elevated temperatures and fluences. Our results provide a starting point for experimental optical control of magnetism in MAX phases, bringing this broad class of materials into modern 2D spintronics.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Protocol yields inertial and damping constants for PbTiO3

Effective dynamic constants for nonequilibrium third-principles simulations

Extracted from atomistic simulations, the constants support more accurate mesoscale models of ferroelectric nonequilibrium behavior.

Figure from the paper full image
abstract click to expand
Computational studies of the thermodynamic properties of materials at the mesoscopic and macroscopic scales -- involving lengths and times of at least $\mu$m and $\mu$s, respectively -- rely on a coarse-graining approximation such that only a few relevant collective variables are treated explicitly. Those variables typically take the form of fields defined everywhere in space or macroscopic quantities when spatial inhomogeneities can be treated implicitly. The free energy is usually expressed as a Landau-like potential whose temperature-dependent minima track stable states, characteristic equilibrium fluctuations being implicitly accounted for. Further, the response of the system to external perturbations, and its relaxation toward thermal equilibrium, are described in terms of simple equations of motion governed by effective inertial and viscous-damping constants. There is considerable literature on the problem of deriving Landau free energy potentials, from either experiment or predictive atomistic simulations, including recent efforts to develop systematic machine-learning approaches that we denote ``third principles''. Much less attention has received the calculation of the effective constants controlling the nonequilibrium macroscopic or mesoscopic dynamics. Here we tackle that problem, describing a protocol that allows us to compute the temperature-dependent inertial and damping coefficients associated to the electric polarization in representative soft-mode ferroelectric PbTiO$_{3}$. Our scheme lends itself to a widespread application, although the non-trivial behaviors found in PbTiO$_{3}$ suggest that more case studies will be needed to finetune a general and robust calculation protocol. Our results also allow us to comment on common assumptions in the literature of effective dynamic treatments of ferroelectrics and related materials.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Curved hBN boosts quantum emitter coherence at room temperature

Strain-Enhanced Coherence in Curved hBN Quantum Emitters

Strain from thermal bubbles depletes phonons to yield Debye-Waller factors of 0.91 in ambient conditions.

Figure from the paper full image
abstract click to expand
Hexagonal boron nitride (hBN) hosts robust room-temperature single-photon emitters, yet their coherence is typically limited by phonon induced dephasing and spectral broadening. Here, we show that thermally induced curvature in bulk like hBN flakes provides a strain enabled route to suppress defect phonon coupling under ambient conditions. Nanoscale bubbles formed by thermal processing generate strong through thickness strain gradients, which we directly probe by infrared nano spectroscopy. These measurements reveal strain induced splitting of in-plane phonon modes, evidencing a substantial local modification of the phonon density of states. Quantum emitters localized within these curved regions exhibit markedly enhanced room temperature spectral purity, with Debye Waller factors of 0.91 and narrower line widths than emitters in flat regions. Photon correlation measurements confirm high-purity single photon emission at room temperature. Supported by first-principles calculations, we attribute this behavior to strain driven phonon redistribution, which depletes phonons in tensile regions and accumulates them in compressive regions, thereby creating locally phonon suppressed environments for defect emitters. These results establish strain engineering as an effective route for phonon control in hBN and open a pathway toward high coherence, room-temperature quantum light sources for integrated nano photonic platforms.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Anode-free Li/Cu batteries sit 5% from saddle-node instability threshold

Saddle-node bifurcation in interfacial morphology selects battery degradation phase

Model maps four anode types to stability phases and predicts narrow operational window for nucleation-controlled deposition

Figure from the paper full image
abstract click to expand
We propose a minimal nonlinear closure ODE for the dynamic active-area factor of a battery interface and show that it exhibits a saddle-node bifurcation when the smoothing rate saturates with surface roughness. The closure is the simplest physically motivated extension of a recently introduced single-fixed-point closure [C. Bae, in preparation (2026)]: u = K - u/(1 + alphau^2), where u = xi - 1 is the dimensionless excess active area, K the dimensionless drive, and alpha a single saturation parameter. The bifurcation occurs at K_c = 1/(2sqrt(alpha)), separating a smooth passivating phase from a morphologically unstable phase. Mapping four canonical anode configurations -- graphite, silicon composite, lithium metal, and anode-free Li/Cu -- onto the closure via end-of-cycling steady-state xi extracted from publicly available long-cycle data populates the stable branch with monotonically increasing K/K_c ratios: graphite (~0.01), silicon composite (~0.24), lithium metal (~0.73), and anode-free (~0.95). The anode-free configuration sits within 5% of the saddle-node threshold, predicting a vanishingly small operational stability window in current density, temperature, and electrolyte composition. We test three falsifiable predictions of the framework -- a critical current density, a critical temperature shift, and a mean-field critical-slowing-down exponent -- and find them broadly consistent with publicly available data. We argue that this near-critical position is universal to nucleation-controlled deposition on non-passivating substrates.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Battery anodes show universal parabolic interphase loss in three chemistries

Parabolic-growth universality and its nucleation-driven breakdown across lithium-battery anode chemistries

Data from graphite, silicon and lithium metal follow the same square-root scaling, but anode-free cells deviate toward nucleation control, 0

Figure from the paper full image
abstract click to expand
Solid-electrolyte interphase (SEI) growth is widely modeled cell-by-cell with chemistry-specific closures, yet its underlying kinetic scaling is rarely tested across chemistries. By compiling cycle-resolved data from public long-cycle datasets covering four anode configurations -- graphite, silicon composite, lithium metal, and anode-free -- we show that the cumulative interphase-loss index Lambda_int obeys the parabolic law Lambda_int = A_chem * sqrt(1 - Theta_Li) in three of the four chemistries, with an exponent indistinguishable from alpha = 1/2 within experimental uncertainty. The chemistry-specific prefactor A_chem spans an order of magnitude, but the diffusion-limited parabolic kinetics is preserved. The fourth chemistry, anode-free configurations, deviates with a super-parabolic exponent alpha approx 0.77, consistent with a nucleation-controlled growth regime. We rationalize the result using the Tammann-Deal-Grove parabolic-growth framework adapted to interphase formation and identify the conditions under which universality is recovered. The observed regularity reduces SEI modeling complexity to a single rate constant per chemistry and provides a sharp falsifiable test for next-generation cell formats.
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cond-mat.mtrl-sci 2026-05-12 2 theorems

Local segregation lowers alloy energy by offsetting atomic strains

Non-homogeneous structure of complex concentrated alloys: Effect of intrinsic strain

Regions with different compositions form so that tensile and compressive fields from varying atom sizes cancel, reducing total system energy

abstract click to expand
Even if the atoms of a multicomponent alloy occupy a common lattice, their distribution is not homogeneous, and regions with different compositions can be detected. Three representative examples will be discussed: a Cantor-type system containing transition-metal elements (Cr, Mn, Fe, Ni, and Co), a refractory high-entropy alloy (Ti, Zr, Nb, Ta, and Mo), and a multicomponent system combining transition and refractory metals (Cu, Ni, Ti, Zr, and Hf). Using a combination of theoretical analysis and experimental observations, we demonstrate that the formation of locally segregated regions can lead to a reduction in the overall energy of the system. This stabilization arises from the compensation of tensile and compressive strain fields associated with atoms of different sizes, highlighting the key role of local chemical and structural heterogeneity in determining the thermodynamic stability of multicomponent alloys.
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cond-mat.mtrl-sci 2026-05-12 Recognition

Host cation identity sets ytterbium charge states in fluoride crystals

Ytterbium charge state and stabilization in the Ba(Ca)F₂ host by electron paramagnetic resonance and infrared photoluminescence

BaF2 promotes perturbed Yb3+ sites while CaF2 keeps unperturbed environments, separating long-range stability from local optics.

Figure from the paper full image
abstract click to expand
Lanthanide-doped fluorides are promising materials for advanced photonic and quantum applications due to their wide bandgap, low phonon energy, and chemical stability. In this work, we present a systematic comparative study of ytterbium incorporation at low doping levels (0.05--0.2 mol\%) in BaF$_2$ and CaF$_2$ single crystals, focusing on the interplay between host lattice properties, charge-state stabilization, and defect formation mechanisms. Using a combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), transmittance, and infrared photoluminescence (IR PL), we explore how host lattice properties affect the stabilization of Yb$^{3+}$ and Yb$^{2+}$ ions. XRD confirmed cubic phase purity and lattice parameter stability in both hosts, while XPS revealed surface chemical composition variations associated with charge-compensating defects and trace impurities. EPR spectra indicated that BaF$_2$ favored perturbed Yb$^{3+}$ environments with increasing dopant levels, while CaF$_2$ maintained predominantly unperturbed sites, suggesting a more favorable ionic match for Yb$^{2+}$. Photothermal deflection spectroscopy (PDS) and IR PL results showed host-specific optical responses, with CaF$_2$ exhibiting crystal-field splitting and broader local field effects. These results reveal a clear decoupling between long-range structural stability and local lattice perturbations, and demonstrate that host cation identity governs the balance between Yb$^{2+}$ and Yb$^{3+}$ stabilization as well as defect-driven optical behavior. This offers valuable insights for optimizing rare-earth-doped fluoride crystals in laser, scintillator, and quantum device applications.
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cond-mat.mtrl-sci 2026-05-12 Recognition

Magnetization and chirality leave excited-state lifetimes unchanged

Chiral Porphyrin Monolayers on Ferromagnetic Thin Films: Ultrafast Spectroscopy of Hybrid Interfaces

Femtosecond spectroscopy of porphyrin monolayers on gold-capped Co/Ni films finds shorter lifetimes from surface contact but no effect from磁

abstract click to expand
Hybrid ferromagnetic metal/organic interfaces (spinterfaces) exhibit unique properties, including spin filtering. In parallel, chiral organic molecules can themselves induce efficient spin filtering, leading to unexpectedly high spin polarizations. Here, we investigate how the proximity of gold-capped Co/Ni ferromagnetic multilayers influences the spectroscopic properties and photoinduced electron dynamics of chiral oligopeptides bearing a porphyrin chromophore. The molecules are covalently attached to the gold cap via a chiral linker, forming a self-assembled monolayer. The porphyrin macrocycles adopt an orientation parallel to the surface, resulting in the formation of J-like aggregates. Photoinduced dynamics are probed using femtosecond pump-probe transient absorption spectroscopy. Despite excitation of only a single molecular layer, a clear transient absorption signal of the porphyrin singlet excited state is observed. Adsorption on the metal surface leads to a pronounced reduction of the excited-state lifetime. However, no signatures of long-lived photoinduced charge-transfer products are detected. Furthermore, no dependence of the excited-state dynamics on either the magnetization direction of the ferromagnetic layer or the molecular chirality is observed.
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cond-mat.mtrl-sci 2026-05-12 1 theorem

Janus monolayers host valley-specific spin textures

Valley-contrasting Spin Textures in Janus Metal Phosphochalcogenides

Ising type at K valleys and mixed Weyl-Rashba at Gamma, with strain-tunable gaps and valley-dependent Hall currents.

Figure from the paper full image
abstract click to expand
Momentum-resolved spin textures and potential valley-contrasting physical properties in the momentum space are two intriguing characteristics of noncentrosymmetric materials, and they have broad applications in spintronics and valleytronics. The realization of diverse spin textures within a single material, along with their further coupling to the valley degree of freedom, is highly desirable. Via first-principles calculations, we investigate electronic properties of Janus MP$_2$S$_3$Se$_3$ monolayers, which exhibits distinct spin textures at different valleys. While Ising-type spin textures are located at $K_\pm$ valleys, the symmetry breaking from the Janus structure brings about a coexistence of Weyl-type and Rashba-type spin textures at $\Gamma$ valley. In addition to valley-contrasting spin textures, valley dependence also occurs in Berry-curvature-driven anomalous Hall currents and optical selectivity. Besides, energy differences between $\Gamma$ and $K_\pm$, as well as band gaps, are highly tunable by applied strain. These findings present an intriguing coupling between diverse spin textures and multiple valleys, and pave the way for designing advanced electronic devices that leverage spin and valley degrees of freedom.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Sliding tunes MXene heterostructures into quantum anomalous Hall phase

Giant Rashba Splitting and Enhanced Nonlinear Berry-Phase Responses in Sliding-Tunable vdW MXene Heterostructures

Lateral sliding and stacking inversion control exchange-SOC interplay, enabling mechanical tuning of Rashba splitting and emergent QAH state

Figure from the paper full image
abstract click to expand
Chalcogen-terminated van der Waals MXenes (M2CX2; M = Nb, Ta; X = S, Se) provide a robust platform for exploring strong spin-orbit coupling and proximity engineering. To probe their tunability and guide optimization of emergent properties, we systematically examine sister compounds and propose M2CS2/CrBr3 heterostructures that break time-reversal symmetry via proximity exchange coupling, enabling combined intrinsic magnetic and mechanical control. First-principles calculations reveal Rashba splitting up to 2.53 eV A and valley-contrasting spin polarization in monolayers. These features drive strong second-order nonlinear responses, with pristine bilayer Ta2CS2 reaching a shift current of |sigma|_max approx 5 A mA/V^2 and Nb2CS2/CrBr3 attaining |D|_max approx 18.44 A. In M2CS2/CrBr3 heterostructures, the ferromagnetic substrate induces a magnetization-reversible proximity exchange field with valley-selective conduction-band renormalization (Delta_val approx 50 meV). Crucially, interfacial geometry, controlled by stacking inversion and lateral sliding, acts as a mechanical knob that continuously tunes the exchange-SOC interplay and bandgap, driving an emergent quantum anomalous Hall phase in the bilayer.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Nitrogen forms N₂ molecules in implanted β-Ga₂O₃

Molecular Nitrogen Formation in Nitrogen-Implanted (100) β-Ga₂O₃ Revealed by Temperature-Dependent N K-edge XANES

X-ray spectra show implanted atoms bond to each other instead of creating holes, explaining failed p-type doping attempts.

abstract click to expand
The realization of $p$-type doping in wide-band-gap oxide semiconductors remains a major challenge, particularly in $\beta-Ga_2O_3$ where nitrogen has long been considered a potential acceptor dopant but has consistently failed to produce hole conductivity. Here we investigate the microscopic configuration of implanted nitrogen in (100) $\beta-Ga_2O_3$ using temperature-dependent $N$ $K$-edge x-ray absorption spectroscopy. The spectra reveal a pronounced $\pi^*$ resonance characteristic of molecular nitrogen, which becomes increasingly dominant upon thermal annealing. First-principles calculations and multiple-scattering simulations reveal a pronounced tendency for nitrogen atoms to form $N-N$ bonded configurations in the $Ga_2O_3$ matrix, particularly in defect-rich environments created by ion implantation, reproducing the characteristic spectral features observed in the $N$ $K$-edge XANES spectra. Structural analysis further indicates that implantation induces a defect-rich near-surface layer with local $\beta$-to-$\gamma$-like structural motifs, highlighting the strongly nonequilibrium structural environment in which nitrogen incorporation occurs. Reported results show that implanted nitrogen preferentially forms molecular $N_2$-like configurations rather than substitutional acceptors. Our results provide a microscopic explanation for the long-standing failure of nitrogen acceptor doping in $\beta-Ga_2O_3$ and reveal dopant molecularization as a previously overlooked pathway for impurity incorporation under strongly nonequilibrium implantation conditions.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

ABC stacking maximizes ZT in Sc2Si2Te6

Stacking-dependent thermoelectric transport in layered Sc₂Si₂Te₆ from first principles

Layer arrangement changes conduction-band degeneracy and phonon scattering, giving ABC the best performance and AA the worst.

Figure from the paper full image
abstract click to expand
Stacking polymorphism is a common characteristic of van der Waals layered materials and can substantially modify their physical properties. Here, based on first-principles calculations combined with electron and phonon transport theories, we systematically investigate the thermodynamic stability, electronic structure, lattice dynamics, and thermoelectric performance of Sc_2Si_2Te_6 with three high-symmetry stacking sequences, namely, AA, AB, and ABC. We find that the AA- and AB-stacked structures are nearly degenerate in energy with the experimentally reported ABC phase, and that the maximum sliding barrier among these stacking sequences is only about 10~meV/atom, thereby accounting for the stacking faults observed experimentally. These three stacking sequences exhibit distinct electronic structures, with the conduction-band minimum being highly sensitive to the stacking sequence. As a consequence, the conduction-band degeneracies are 12, 2, and 8 for the ABC, AA, and AB stackings, respectively, leading to markedly different electronic transport properties near the band edge. The lattice thermal conductivity is governed primarily by three-phonon scattering, whereas four-phonon scattering provides an additional reduction, particularly in the ABC stacking. Among the three structures, the AB stacking exhibits the lowest lattice thermal conductivity owing to its stronger three-phonon scattering and lower phonon group velocity. As a result, the maximum thermoelectric figure of merit, ZT, is achieved in the ABC structure, followed closely by the AB structure, whereas the AA structure shows a substantially reduced value. These results demonstrate that the stacking sequence exerts a non-negligible influence on the thermoelectric performance of Sc_2Si_2Te_6 and suggest that suppressing the formation of the AA stacking is important for achieving high thermoelectric performance.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

ECCI workflow reveals mixed dislocations in olivine subgrain boundaries

Characterizing Dislocation Substructures in Creep-Deformed Olivine Using Electron Channeling Contrast Imaging

The method images larger areas than TEM and shows non-planar boundaries containing several dislocation types at once.

abstract click to expand
Olivine is the dominant mineral in Earth's upper mantle and therefore controls mantle rheology and the mechanics of plate tectonics. The constitutive laws for dislocation-mediated deformation of olivine depend on the nature, density, and arrangements of dislocations within crystals. Hence, imaging and characterizing these defects is important, albeit challenging. Traditional imaging approaches involve (1) transmission electron microscopy (TEM), which samples small areas and requires extensive preparation and (2) oxidation decoration methods that have low spatial resolution and cannot distinguish dislocations of opposite Burgers vectors. Here, we apply electron channeling contrast imaging (ECCI) to unlock insight into the deformation structures within olivine, and combined with electron backscatter diffraction (EBSD) and weighted Burgers vector (WBV) mapping as an informative route to characterize dislocation substructures in bulk materials. Specifically, we have used an ECCI workflow based on selected-area electron channeling patterns (SA-ECPs) and we apply this workflow to a single crystal of San Carlos olivine that was deformed by creep at high temperature. ECCI micrographs reveal subgrain boundaries, surface threading dislocations, and dislocation loops across representative areas. The observations demonstrate that this workflow can reliably reveal the complexity of subgrain boundaries in olivine, which can host multiple dislocation types and exhibit non-planar geometries. Despite the limited number of slip systems in olivine, subgrain boundaries can form complex, mixed assemblies. Overall, such observations can provide a variety of constraints on dislocation types, morphologies, and distributions, which are required to parameterize and calibrate models of transient and steady-state dislocation creep in olivine and other materials.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Cu(100) EFG varies linearly with temperature from ionic relaxation

First-Principles Study of the Temperature Dependence of Structural, Electronic, and Hyperfine Properties of the Cu(100) Surface

DFT calculations using bulk lattice parameters tie the dependence to anisotropic surface relaxation that breaks cubic symmetry.

abstract click to expand
In this work, we investigate the temperature-dependent behavior of the pure (undoped) Cu(100) surface using first-principles calculations within the Density Functional Theory framework. One of the main objectives is to determine whether the linear dependence of the predicted electric-field gradient (EFG) tensor on the outermost Cu atom on the Cu(100) surface arises from the same generation of the surface or from the reconstruction of the surface. To this end, we perform here a comprehensive $\it{ab}$ $\it{initio}$ study of the Cu(100) surface reconstruction and its associated structural, electronic, and hyperfine properties as a function of temperature, not only at the outermost atomic layer (i.e., the topmost Cu atom) but also as a function of atomic depth relative to the reconstructed surface. To study the temperature dependence of the EFG, we use experimentally determined temperature-dependent lattice parameters for bulk copper in our calculations. The anisotropic relaxation that arises when bulk symmetry is broken helps unravel the potential sources of EFG temperature dependence at the surface. Studying the electron density of conduction electrons $\rho$($\bf{r}$) at the atomic scale near the Cu nucleus and the atom-resolved partial density of states at the topmost Cu atom allows us to correlate the surface effect on the EFG with the bulk value. Finally, we correlate the temperature dependence of the EFG on the undoped Cu(100) surface with the linear behavior of the ''ionic'' contribution to the EFG.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Stark spectra keep 3:1 peak spacing ratio as field rises

Universal 3:1 Scaling of Quantum-Confined Stark Spectra Revealed by a Three-Dimensional Profile

Sub-bandgap and above-bandgap spacings in quantum wells follow fixed scalings set by well width and masses, independent of electric field.

Figure from the paper full image
abstract click to expand
We report that the quantum-confined Stark effect spectrum exhibits a nearly rigid redshift while preserving its characteristic peak spacing patterns when increasing the electric field strength F. Using InGaN as a model system, we uncover two electric-field-independent scaling laws for the spectral peaks in both the sub-bandgap and above-bandgap regions and the coefficient ratio is near 3:1. With a novel three-dimensional (3D) visualization, we reveal that the sub-bandgap peak spacings scale as $\frac{12\pi\hbar^2}{L^2\sqrt{m_em_h}}$ while the above-bandgap peak spacings scale as $\frac{4\pi\hbar^2}{L^2\sqrt{m_em_h}}$, explaining the origin of the 3:1 ratio. This scaling behavior, validated in both InGaN and GaAs systems and at electroluminescence working conditions, shows that increasing F only expands the energy range and increases the number of peaks without altering the spacing. Beyond these laws, the 3D profile offers new insights into the Tauc background, Franz-Keldysh oscillations and coherence length, providing a powerful tool for the design and diagnostics of electro-optic devices.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

SiNx layer boosts diamond/GaN band offsets by 0.42 eV

Band alignment of grafted diamond/GaN p-n heterojunctions interfaced with ALD Al2O3 and SiNx/Al2O3

The added dielectric modifies the interfacial electrostatic potential, enabling tunable rectifying p-n diodes.

Figure from the paper full image
abstract click to expand
Diamond and gallium nitride are complementary semiconductors for forming p-n junctions because of their respective doping limitations. Understanding the band alignment of grafted diamond/GaN heterojunctions is therefore essential for optimizing diode performance. In this study, the band alignment of diamond/Al2O3/GaN and diamond/Al2O3/SiNx/GaN heterostructures was determined by X-ray photoelectron spectroscopy. Both structures exhibit type-II band alignment, but with different band offsets. The band offsets of the diamond/Al2O3/SiNx/GaN heterojunction are larger by 0.42 eV than those of diamond/Al2O3/GaN. This difference is attributed to a modification of the interfacial electrostatic potential, which may arise from a reduced density of positive fixed charges in the interfacial dielectric near the diamond/Al2O3 interface after insertion of the SiNx layer. These results demonstrate that interfacial-layer engineering provides an effective strategy for tailoring the band alignment of grafted diamond/GaN heterojunctions, offering guidance for the design of p-n diodes with tunable rectifying characteristics.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Diamond surface phonons stable within 1.6% over 10-300 K

Angle-Resolved Cryogenic Brillouin-Mandelstam Spectroscopy of Surface and Bulk Acoustic Phonons in Diamond

Angle-resolved spectroscopy confirms theory for Rayleigh, shear, and pseudo-longitudinal modes, supporting quantum sensor design.

abstract click to expand
We used angle-resolved Brillouin-Mandelstam light-scattering spectroscopy to monitor surface and bulk acoustic phonons in diamond along the <100> and <110> crystallographic directions across a temperature range from 10 K to 300 K. The frequencies and phase velocities were measured for three types of surface acoustic phonons: Rayleigh waves, shear horizontal waves, and high-frequency pseudo-longitudinal waves. All surface acoustic phonons exhibit weak temperature dependence, with the largest observed change of 1.6% across the examined temperature range. The frequencies of all three types of surface acoustic phonons agree with the theoretical values within the experimental uncertainty. Cryogenic surface-acoustic-phonon data are important for diamond-based quantum sensors, surface acoustic wave devices, and other electronic technologies. Knowledge of surface acoustic phonons can also be used for developing accurate models for thermal transport between interfaces.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

MLIP representation alignment improves crystal generator stability

CrystalREPA: Transferring Physical Priors from Universal MLIPs to Crystal Generative Models

Contrastive transfer of atom-wise priors raises thermodynamic stability, validity, and fidelity with no inference cost added.

Figure from the paper full image
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Crystal generative models mainly learn what stable crystals look like, with little explicit supervision for what makes them stable. We reveal a substantial representation gap between state-of-the-art crystal generative models and pretrained universal machine learning interatomic potentials (MLIPs) via energy probing, and show this gap can be closed by a simple training-time alignment. We propose Crystal REPresentation Alignment (CrystalREPA), a plug-and-play framework that aligns the atom-wise hidden states of generative encoders with frozen MLIP representations through an element-aware contrastive objective, transferring stability-aware atomistic priors with marginal training overhead and no additional inference cost. Across three generative frameworks, ten MLIP teachers, and two benchmark datasets, CrystalREPA consistently improves the thermodynamic stability, structural validity, and structural fidelity of generated crystals. Equally important, we find that an MLIP's transfer effectiveness is poorly predicted by its accuracy on standard leaderboards (e.g., Matbench Discovery) but strongly predicted by the distinguishability of its atom-wise representation space, yielding a practical, accuracy-independent criterion for selecting MLIP teachers for generative transfer.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Wannier modes localize vibrations to quantify bond strengths in solids

Bond strengths in solids computed from a Wannier-type construction of local vibrational modes

Superpositions of wavevector modes produce real-space forces that incorporate dispersion effects for crystal bonding analysis.

Figure from the paper full image
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We introduce a Wannier-type formulation of periodic local vibrational mode theory that yields real-space-localized vibrational modes associated with individual internal coordinates in crystalline solids. These modes are constructed as locally coherent superpositions of wavevector-resolved local modes, yielding a smooth and gauge-consistent real-space representation without the need for additional phase-fixing procedures. The resulting Wannier-type local modes provide well-defined force constants and frequencies that enable robust, chemically interpretable measures of bond and interaction strengths in periodic systems. Moreover, our framework demonstrates that phonon dispersion behavior makes important contributions to the bond and interaction strengths calculated via local vibrational mode theory. We demonstrate the method for representative ionic and covalent systems, including MgO, tetrahedrally-coordinated C, Si, SiC, and two polymorphs of CaCO3. Our framework establishes a direct analog of molecular local modes for fully periodic systems and opens new avenues for quantitative bonding analysis in crystalline materials.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Structural change shifts Curie temperature by 50 K in Heusler alloys

Thermodynamic Approach for Deciphering Magneto-Structural Phase Transitions: Proof of Concept in Heusler Alloys

Thermodynamic model extracts separate austenite and martensite ordering temperatures from standard magnetization curves

Figure from the paper full image
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Ferromagnetic solids acquire nontrivial magnetic and caloric properties when the temperature of the structural phase transition approaches the Curie point. Deciphering magneto-structural transitions, i.e. determining their characteristic temperatures and elucidating the related properties, remains challenging. In the present paper, three types of transformational behaviour of Ni50Mn25-xCuxGa25 (x = 6.25, 6.5, 6.75, 7) and Ni50.5Mn18.5Cu6.5Ga24.5 alloys have been identified, arising from small variations in chemical composition: (i) structural martensitic transformation (MT) in the ferromagnetic phase; (ii) magneto-structural phase transition from paramagnetic austenite to ferromagnetic martensite; (iii) MT in paramagnetic phase. The temperature-dependent values of magnetization, M(T), and of magnetic susceptibility, $\chi(T)$, were measured for each alloy. A novel thermodynamic analysis was used to determine the Curie points and MT temperatures. The novelty lies in considering the interplay between structural and magnetic characteristics of the alloys through the impact of the structural transition on the spin-exchange parameter. The theoretical analysis of experimental data revealed that this impact results in a large difference ($\geq$ 50 K) between the Curie temperatures computed for the austenitic and martensitic states of each alloy. The characteristic temperatures, corresponding to the extrema of the dM(T)/dT and $\chi(T)$ functions, were calculated. The correlation of these temperatures with the Curie temperatures and the MT temperatures is not straightforward and depends strongly on the type of transformational behaviour (i) - (iii). The proposed approach provides a robust framework for extracting unmeasurable characteristic temperatures from standard magnetization data, applicable to ferromagnetic Heusler systems and other multiferroic ferromagnetic materials.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Screening identifies 45 stable high-entropy MBenes for CO2 reduction

Multi-Fidelity Computational Screening of High-Entropy MBenes for CO₂ Electroreduction

DFT-trained ML potential rapidly checks disordered surfaces and finds candidates with negative formation energies and viable CO2-to-CO steps

Figure from the paper full image
abstract click to expand
High-entropy MBenes (HE-MBenes) represent a promising, unexplored class of 2D materials for electrocatalysis. In this work, we present a systematic computational screening of 56 equiatomic quinary HE-MBene compositions from the {Ti, V, Cr, Mo, Nb, Ta, Zr, Hf} pool for CO$_2$ adsorption and electroreduction. Using the Monte Carlo Special Quasirandom Structure (MCSQS) algorithm, we generated disordered M$_1B_1$-type supercells and assessed structural stability via DFT (PBE+D3) in VASP. Of the 56 candidates, 55 passed relaxation, with 45 exhibiting negative formation energies, confirming thermodynamic stability. To efficiently screen CO$_2$ adsorption across disordered surfaces, we developed a machine-learning interatomic potential (MLIP) using the MACE architecture. Fine-tuned on our DFT dataset, the model achieved energy RMSEs of 3.49 and 3.0 meV/atom for adsorbed and pristine sets, respectively. Active sites were identified via PDOS analysis, matching metal d-orbital signatures with CO$_2$ molecular orbitals. The rate-determining step of the CO$_2$-to-CO pathway was evaluated using the computational hydrogen electrode (CHE) model. Short-time structural integrity was assessed via AIMD at 500 K over 2.5 ps; phonon-based stability remains a priority for future work. Our results establish an integrated DFT-MLIP-AIMD framework for the rational design of high-entropy 2D materials tailored for CO$_2$ conversion.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Steels solidify via an intermediate superite phase

The superite phase and phase transition inducing multiscale solidification microstructures and segregations in steels

Liquid first forms superite dendrites that then convert to solid phases while expelling solutes, producing multiscale structures and segrega

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Based on classical concept, solidification of alloys is a direct transition from liquid phase to solid phase, by which dendrites and dendritic segregation are produced. Through in-situ and real time morphology observation and XRD test during solidification of three steels, a new superite phase featured as statistically oriented tiny structures was identified, and a general liquid-superite-solid phase transformation process is revealed. In the early solidification stage, the liquid alloys transit to dendrites composed of superite phase. Initiated from the boundaries of dendritic arms or dendrite grains, the superite phase transits to austenite grains within an initial dendritic arm, and expels solute elements to the residual superite phase. Mixed multi-phase microstructures are subsequently produced from the residual enriched superite phase. Here, although three steels exhibit different phase proportion and phase constitution in the superite-solid transition, they all follow above general transition mode. Multiscale microstructures and segregations are produced in the transition from superite to solid. These new findings change the basic understanding about the solidification of alloys, rediscover the formation mechanism on segregations and multiscale solidification microstructures, including dendrite pattern, solid dendritic arm, dendritic segregation, the mixed multi-phase microstructures, eutectic, inclusions and precipitate. These new findings are also crucial to the control of solidification microstructures and segregation in metals.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Neural operators transfer information across material scales

Multiscale modeling of materials and neural operators

Discretization-independent mappings preserve essential physics when moving between length and time scales in three examples.

Figure from the paper full image
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Multiscale modeling is essential for understanding the complex behavior of materials. However, accurately transferring all relevant information from one scale to another has remained an outstanding challenge. Neural operators, discretization-independent generalizations of neural networks, is proving to be a powerful tool in addressing this challenge. This article provides an introduction to neural operators, and illustrates their use in multiscale modeling of materials through three selected examples.
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cond-mat.mtrl-sci 2026-05-11 1 theorem

Layered Br-I ordering blocks defect diffusion across perovskite planes

Anisotropic Defect Diffusion in Layered CsPbBr_xI₃-x Perovskites

Simulations show easy in-plane migration but strong suppression between layers from strain and local bonding.

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Mixed-halide perovskites offer a route to enhance phase stability and modify optoelectronic properties. Here, we use large-scale molecular dynamics simulations with a reactive force field to investigate defects in CsPbBr$_\mathrm{x}$I$_\mathrm{3-x}$ perovskites, focusing on how defect mobility can be controlled and the stability of the material may be improved by layered ordering of Br and I anions in layers. Our results show that layered halide ordering induces strongly anisotropic defect diffusion: migration proceeds readily along the layers, whereas diffusion across them is strongly suppressed. For Cs defects, this anisotropy originates from directional lattice strain and the associated octahedral tilting, while halide migration is governed by an interplay between strain and preferential local halide bonding configurations.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Layered Br/I ordering blocks defect diffusion across perovskite layers

Anisotropic Defect Diffusion in Layered CsPbBr_xI₃-x Perovskites

Simulations find defects move readily within layers but are strongly suppressed perpendicular to them due to strain and bonding effects.

Figure from the paper full image
abstract click to expand
Mixed-halide perovskites offer a route to enhance phase stability and modify optoelectronic properties. Here, we use large-scale molecular dynamics simulations with a reactive force field to investigate defects in CsPbBr$_\mathrm{x}$I$_\mathrm{3-x}$ perovskites, focusing on how defect mobility can be controlled and the stability of the material may be improved by layered ordering of Br and I anions in layers. Our results show that layered halide ordering induces strongly anisotropic defect diffusion: migration proceeds readily along the layers, whereas diffusion across them is strongly suppressed. For Cs defects, this anisotropy originates from directional lattice strain and the associated octahedral tilting, while halide migration is governed by an interplay between strain and preferential local halide bonding configurations.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Multi-task model simulates phonon splitting and hysteresis out of the box

MatterSim-MT: A multi-task foundation model for in silico materials characterization

Pretrained on 35 million structures, it matches experiments on SiC, BaTiO3 and Li-rich cathodes without separate task training

abstract click to expand
Accurate property characterization is a major bottleneck in materials design. While first-principles methods and task-specific machine-learning models have driven important progress, they remain fundamentally limited in scalability and generalizability across the vast space of structures and properties relevant to real-world materials design. We present MatterSim-MT, a multi-task foundation model for in silico materials simulation and property characterization. The model is pretrained on over 35 million first-principles-labeled structures covering 89 elements, temperatures up to 5000 K and pressures up to 1000 GPa, and is fine-tuned on various properties including Bader charges, magnetic moments, Born effective charges, and dielectric matrices. Out of the box, MatterSim-MT not only serves as a foundation model for predicting material structure, dynamics and thermodynamics, its multi-task architecture also enables a wide range of complex simulations that cannot be captured by potential energy surfaces alone. For example, we demonstrate pressure-dependent LO-TO phonon splitting in SiC with close agreement with experiment, electric hysteresis in ferroelectric BaTiO3, and the cationic-to-anionic redox transition during delithiation of a Li-rich cathode material. Finally, we show that MatterSim-MT scales well with more data and parameters, can be efficiently fine-tuned to higher levels of theory, and can be efficiently extended to new systems via active learning. Overall, we believe this approach provides a scalable route to accurate in silico materials characterization.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Rough gold contacts boost photocurrents in WS2

Interfacial control of hot-carrier extraction and photostability in two-dimensional materials

Imbalanced electron and hole transfer speeds deliver higher net currents and ambient stability without encapsulation.

abstract click to expand
Two-dimensional transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, yet their implementation is hindered by limited sample stability and challenges in forming reliable electrical contacts. Here, by utilizing time-domain THz emission spectroscopy we directly probe charge carrier dynamics in monolayer WS2 on gold (Au) and fused silica (SiO2) as a function of interface morphology. For laser excitation above the band gap of WS2, we independently extract effective transport times for both electrons and holes and find that discontinuous WS2 contacts on rough Au generate larger net photocurrents than uniform, strongly coupled interfaces - a counterintuitive observation attributed to imbalanced electron and hole transfer from WS2 to Au. Crucially, we demonstrate that ultrafast charge extraction and separation suppress recombination-driven energy release and thereby prevent photo-induced degradation under ambient conditions, eliminating the need for encapsulation. These findings redefine interfacial design as a central control parameter for both performance and stability in 2D optoelectronic devices.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Kagome magnet shows 0.29 e²/h intrinsic Hall conductivity per layer

Anomalous magnetotransport in a non-collinear correlated kagome ferromagnet MgMn6Sn6

The value stays nearly constant with field direction while low-temperature scattering becomes strongly anisotropic, alongside a large Sommer

Figure from the paper full image
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Magnetic kagome metals provide a fertile platform for exploring unusual magnetotransport phenomena arising from the intricate interplay between electronic topology, electron correlations, and magnetic order. MgMn6Sn6 is a room-temperature kagome ferromagnet with strong in-plane magnetic anisotropy. Here, we report a combined study of single-crystal neutron diffraction (SCND) and magnetotransport properties of MgMn6Sn6, supported by first-principles calculations. Our SCND measurements reveal a non-collinear arrangement of Mn magnetic moments within the basal plane of the kagome bilayer. The Hall conductivity shows a substantial intrinsic contribution of approximately 0.29 e^2/h per kagome layer, which is nearly isotropic with respect to the field orientation. At low temperatures, the anomalous Hall conductivity develops a pronounced anisotropic extrinsic component, highlighting the directional sensitivity of scattering processes. The significantly large value of the Sommerfeld coefficient, in the absence of f-electrons, underscores enhanced electron correlation. Therefore, the non-collinear kagome ferromagnet MgMn6Sn6 is a promising candidate for studying the effects of electron correlation on magnetotransport properties.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

90-nm ferroelectric domains shape charge extraction in perovskites

Ferroelectric domains in methylammonium lead iodide perovskite thin-films

Piezoresponse force microscopy finds alternating polarization domains that match local photovoltaic response patterns under illumination.

Figure from the paper full image
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We explore the ferroic properties of methylammonium lead iodide perovskite solar cells by Piezoresponse Force Microscopy (PFM). In vertical and horizontal PFM imaging, we find domains of alternating polarization with a width of 90 nm which we identify as polarized ferroelectric domains. High-resolution photo-conductive atomic force micrographs under illumination also show alternating charge carrier extraction patterns which we attribute to the local vertical polarization components within the ferroelectric domains. The correlation of the sample properties with Atomic Force and Kelvin Probe Force Micrographs evidence the piezo-electric nature of the domains.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Tandem cell with Cu2SiSe3 and Cu2SnS3 hits 24.1 percent efficiency

Photovoltaic Possibility of Cu2SiSe3 and Cu2SnS3 Ternary Chalcogenides- Single Junction to Tandem Architecture

Simulations combine the two ternary absorbers to capture visible and infrared light, beating single-junction results.

abstract click to expand
Cu based ternary chalcogenides are gathering attention for sustainable energy applications due to their reduced complexity compared to quaternary alternatives. We used drift diffusion modeling to evaluate the feasibility of photovoltaics employing ternary chalcogenide absorbers based on Cu2SiSe3 and Cu2SnS3. The device metrics are evaluated by analyzing absorber layer thickness intrinsic carrier concentration defect density and energy band alignment at interfacial junctions. The optimized single junction Cu2SiSe3 based device configuration achieves a power conversion efficiency of 18.13 percent exhibiting a short circuit current density of 38 mA cm^-2 and an open circuit voltage of 0.64 V. The Cu2SnS3 based device achieves an efficiency of 15.59 percent with a short circuit current density of 48.8 mA cm^-2 and an open circuit voltage of 0.42 V. We examined the impact of the buffer layer on device parameters uncovering further avenues for performance improvement. Additionally we simulated a two terminal tandem solar cell using Cu2SiSe3 Eg 1.44 eV in the upper cell to capture photons from the visible spectrum and Cu2SnS3 Eg 0.91 eV in the lower cell to absorb from the infrared spectrum. The simulated tandem architecture, featuring a VOC of 1.24 V a JSC of 24.6 mA cm^-2 a fill factor (FF) of 79.2 percent and an efficiency of 24.1 percent markedly surpassed conventional single junction devices demonstrating the viability of Cu2SiSe3-Cu2SnS3 absorber-based tandem solar cells for next generation high-efficiency solar technologies.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Facet distributions flag selective alloys for CO2 hydrogenation

Selectivity- and Activity-Aware Catalyst Descriptors for CO₂ Hydrogenation on Alloy Nanocatalysts using Machine-Learned Force Fields

Resolving crystal faces on alloy nanoparticles links their structure to both reaction activity and preference for methanol.

Figure from the paper full image
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Adsorption energy distributions (AEDs) have emerged as a powerful and increasingly adopted descriptor for catalytic performance in high-entropy alloys and, more recently, in conventional metallic alloy nanocrystal catalysts. By accounting for diverse adsorption sites and crystallographic facets, AEDs more fully represent nanoparticle-based catalytic surfaces and show strong promise for accelerating rational design and discovery of heterogeneous catalysts, especially for CO$_2$ hydrogenation. However, previous approaches have not sufficiently resolved facet-specific contributions, despite the catalytic significance and prevalence of certain Miller planes in nanoscale catalysts, limiting their applicability in predicting activity and selectivity. Here, we introduce an updated facet-resolved framework for predicting catalytic activity, which also enables insight into selectivity toward C1 products. Universal machine-learned force fields trained on Open Catalyst Project data were employed to compute adsorption energetics across 226 experimentally observed metals, binary alloys, and ternary alloys, encompassing 1.4 million adsorption sites on 2,626 crystallographically distinct surfaces. Using statistical and unsupervised learning techniques, we analyzed facet-specific AEDs to identify highly active and methanol-selective facets. Our approach provides insight into the relationship between structure and catalytic performance metrics like activity and selectivity, and presents a set of alloy compositions and their respective surface orientations for experimental validation toward highly selective CO$_2$ hydrogenation.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Beta-bismuthene grows epitaxially on Sb2Te3

Epitaxial growth of beta-bismuthene on Sb2Te3

STM shows bismuth coverage and temperature control island formation while substrate defects appear in the 2D layer.

Figure from the paper full image
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Over the past decades, two-dimensional crystals have attracted considerable interest as promising materials for electronic and optoelectronic applications. Among them, graphene analogs composed of heavy atoms occupy a particularly distinctive niche due to their enhanced spin-orbit interaction. Here, we present an epitaxial heterointerface formed by beta-bismuthene on Sb2Te3, a well-known three-dimensional topological insulator. Using scanning tunneling microscopy, we systematically investigated the effects of Bi coverage and substrate temperature on nucleation processes, island morphology, and atomic structure. In addition, substrate-induced defects were identified throughout the bismuthene lattice.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Amorphous carbon monolayer shows near-zero adsorption sites for hydrogen evolution

Harnessing Structural Disorder: Unraveling Hydrogen Evolution in Monolayer Amorphous Carbon via First-Principles Simulations and Machine-Learned Potentials

ML potentials find 15 percent of sites favorable, tied to seven-membered rings and ripples, suggesting tuning could match noble metals.

Figure from the paper full image
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Disorder and defective coordination in the catalytic plane are crucial for enhancing the Hydrogen Evolution Reaction (HER) on two-dimensional catalysts. Amorphous materials are disordered, making them catalytically adaptive for many reactions. In this work, the HER capabilities of Monolayer Amorphous Carbon (MAC) were studied in comparison with crystalline carbon derivatives, such as pristine graphene (GE) and graphyne derivatives. MAC generated from melt-quench simulations revealed a diverse framework of predominantly sp2 and sp3 carbons with numerous 5-, 6-, and 7-membered rings. Density Functional Theory (DFT) calculations investigated free-energy variations in hydrogen adsorption for each material. According to Sabatier's principle, optimum activity is achieved when the Gibbs free energy (Delta GH) change approaches zero. Crystalline carbon materials possess limited active sites, with beta-graphyne showing the best Delta GH value of +0.34 eV. The adsorption study for MAC was conducted in 30 distinct local environments, where core structural properties were analyzed against varying radii. Calculations showed a Delta GH distribution for MAC ranging from -0.02 eV to +1.35 eV. To evaluate activity across the entire MAC surface, a MACE MLIP foundation model was finetuned, achieving optimal energy and force fitting of 1.67 meV/atom and 29.15 meV/A, respectively. The MLIP predicted Delta GH values from -0.91 eV to +1.70 eV, with approximately 15% of sites exhibiting values below +0.25 eV. Feature analysis revealed that 7-membered rings, curvature, and ripple height enhance HER activity. Our findings suggest that, with careful optimization of local features, MAC can be tuned to compete with noble metal catalysts.
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cond-mat.mtrl-sci 2026-05-11 1 theorem

Dislocations in β-Ga₂O₃ form arrays on (001) planes

Dislocations in (011)-oriented vertical Bridgman β-Ga₂O₃ substrates

X-ray topography links them to domain boundaries with 10^{-5} rad misorientations, separating them from pit-forming defects in epilayers.

abstract click to expand
Dislocation in (011)-oriented $\beta$-Ga$_2$O$_3$ substrates grown by the vertical Bridgman method was investigated using X-ray topography (XRT), combined with X-ray reticulography. Transmission XRT reveals dislocations lying on the (001) plane and extending along [010], forming arrays associated with domain boundaries. Dislocations on the (011) plane were also identified but differ from those responsible for line-shaped pits on (001) epilayers. Reflection XRT shows good agreement with transmission XRT and enables classification of dislocation types based on contrast features. Reticulography confirms domain boundaries with misorientation on the order of 1E-5 rad, providing insight into defect formation relevant to epi-growth and device performance.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Magnetic field relaxes OER scaling limits via spin-lattice coupling

Spin-lattice coupling enables adaptive adsorption in magnetically-driven electrocatalysts

In Ni-Fe oxyhydroxides the field accesses flexible intermediate states that ease energy trade-offs between reaction steps.

abstract click to expand
A major challenge in electrochemistry is to decouple the reactive intermediates of a catalytic cycle to optimise their energies independently. During the oxygen evolution reaction (OER), such energy interdependence results from the need to generate multiple adsorbates at the same site and sets the minimum overpotential. Here, we show that an external stimulus, such as a magnetic field, can relax the scaling relationships between intermediates during the OER. Spectroscopic measurements and Density Functional Theory simulations in Ni-Fe oxyhydroxides reveal that applying a magnetic field alters surface chemisorption and injects structural flexibility at the interface. We interpret these observations as a consequence of stimulated changes in the spin-lattice coupling, which allow access to quasi-degenerate oxygenated intermediates that modulate the reaction energy demands. Our findings redefine the scaling limitations as state-projected rather than intrinsic and establish external stimulation as a strategy to navigate multi-state energy landscapes in electrocatalysis and sensing applications.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Nonpolar crystals switch polarization in quantized steps

Revisiting Ferroelectricity Beyond Polar Space Groups

Multivalued formal polarization permits large changes from ion migration without symmetry breaking, enabling control of charged interfaces.

Figure from the paper full image
abstract click to expand
Ferroelectricity, a hallmark of spontaneous inversion-symmetry breaking, has been a central concept in condensed matter physics and functional materials research, yet recent discoveries are revealing that switchable polarization can emerge in forms far richer than allowed by the conventional symmetry-based paradigm. Fractional quantum ferroelectricity and ionic-conductor ferroelectricity challenge the long-standing association of ferroelectricity exclusively with polar space groups. In this Review, we reconcile these emerging phenomena within the Berry-phase modern theory of polarization. We emphasize that polarization in insulating periodic crystals is not a single-valued vector, but a multivalued lattice quantity defined modulo a polarization quantum. Consequently, nonpolar crystals may possess nonzero formal polarization, and adiabatic paths connecting symmetry-equivalent structures can produce quantized changes in polarization without violating symmetry principles. The symmetry of this multivalued formal polarization is governed by a generalized Neumann principle. We further show that the large polarization changes induced by long-range ion migration in both fractional quantum ferroelectrics and ionic-conductor ferroelectrics can be naturally understood through the topological definition of oxidation state, which links ionic transport to quantized charge transfer and polarization change. We discuss the physical accessibility of these unconventional polarization states, highlighting the roles of switching pathways, boundary conditions, and domain-wall dynamics, particularly in systems such as $\alpha$-In$_2$Se$_3$. Finally, we suggest that the most promising functionality of these materials may lie not in conventional bulk ferroelectric switching, but in the creation and control of charged interfaces and domain walls arising from discontinuities in formal polarization.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Water clusters form on wollastonite past four molecules per cell

Water adsorption on a model silicate surface: wollastonite (100)

Atomic force microscopy and calculations reveal the shift from surface-bound to clustered water as coverage rises on this calcium silicate.

abstract click to expand
Water adsorption on silicate surfaces is a critical yet poorly understood process relevant to, e.g., mineral weathering and cement hydration. This study investigates the structure of water overlayers on a model calcium silicate, the lowest-energy (100) surface of wollastonite (CaSiO3). It combines atomically resolved non-contact atomic force microscopy (nc-AFM), acquired with qPlus sensors and functionalized tips in ultrahigh vacuum (UHV), with density functional theory (DFT) calculations employing the metaGGA r2SCAN+rVV10 functional. Adding incremental doses of water to the sample at cryogenic temperatures produces distinct structures governed by the competition between water-surface and water-water interactions. With two water molecules per surface unit cell, water-surface interactions dominate: In line with previous theoretical predictions, adsorbates follow the surface lattice. As the coverage increases, intermolecular hydrogen bonding competes with bonding to the surface, leading to the emergence of complex, coexisting patterns. While their small energy differences prevent an unambiguous identification of the most stable structure by DFT, the experimentally observed symmetries help constrain plausible structural models. Above a critical density of four water molecules per unit cell, water-water interactions prevail, and water clusters are formed. The results provide an atomic-scale framework for understanding water interactions with calcium silicate surfaces.
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cond-mat.mtrl-sci 2026-05-11 3 theorems

Operator learning creates transferable microstructure simulators

Physics-informed operator learning for transferable energy-dissipative microstructure dynamics

PFNet advances states accurately across compositions and stages for phase-field dynamics, extending to martensite.

abstract click to expand
Phase-field simulations provide mechanistic descriptions of microstructure evolution, but repeated high-fidelity integration over long horizons and broad parameter spaces remains computationally expensive. We present PFNet, a physics-informed neural operator framework that advances microstructural states by learning conditional evolution operators rather than direct correlations. PFNet combines a diffusion-inspired U-Net with periodic padding, entropy-based state conditioning and thermodynamic-parameter modulation to encode boundary consistency, instantaneous ordering state and changes in the free-energy landscape. For Cahn-Hilliard coarsening, PFNet achieves accurate one-step prediction and stable autoregressive rollouts across composition, gradient-energy coefficient, coarsening stage and morphology class, with errors concentrated near diffuse interfaces and topology-changing regions. The same framework extends to a four-channel martensitic-transformation benchmark without martensite-specific redesign. These results indicate that physics-informed operator learning can provide transferable surrogates for phase-field dynamics and broader energy-dissipative dynamical systems.
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cond-mat.mtrl-sci 2026-05-11 2 theorems

Autoencoder on charge density predicts moduli to R2=0.94

Physics Aware Representation Learning on Electronic Charge Density for Materials Property Prediction

Latent 16^4 vectors from 128^3 DFT grids enable fast forecasts of bulk, shear, and Young's moduli plus formation energy across 6000+ inorgan

Figure from the paper full image
abstract click to expand
The fundamental quantity governing the mechanical and thermodynamic properties of a crystalline solid is its electronic charge density. Yet, its direct use for the rapid prediction of materials properties remains challenging due to its high dimensionality. Here, we present a physics-informed deep learning framework that directly predicts mechanical and thermodynamic properties from the three-dimensional electronic charge density derived from density functional theory (DFT). The proposed approach first utilizes a three-dimensional convolutional autoencoder for unsupervised dimensionality reduction, compressing a high-resolution charge-density grid (128 x 128 x 128) into a compact latent representation (16 x 16 x 16 x 16) while preserving physically meaningful features, as confirmed by negligible reconstruction errors across diverse crystal systems. The compressed latent-space representation of charge density is then used by two different regression models for property prediction: Light Gradient Boosting Machine (LightGBM) and Attention-based 3D Convolutional Neural Networks (Att CNN), and their performance is compared. Combining composition-based descriptors (Material Agnostic Platform for Informatics and Exploration or MAGPIE) with electronic charge density data further improves the model accuracy. Using a dataset of about 6059 inorganic compounds spanning multiple crystal symmetries, the models achieve strong predictive performance for bulk modulus K (R2 = 0.94), Young's modulus E (R2 = 0.88), shear modulus G (R2 = 0.87), formation energy Eform (R2 = 0.96), and Debye temperature {\Theta} (R2 = 0.89). This work establishes electronic charge density as a transferable, physics-grounded descriptor for materials property prediction, requiring ~ 1/25 the computational resources of full-fledged DFT calculations.
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cond-mat.mtrl-sci 2026-05-11 Recognition

Fine-tuned open VLM beats GPT and Gemini at fracture morphology

Fine-tuning a vision-language model for fracture-surface morphology recognition

Specialist reaches 0.92 precision on 100-image benchmark after training on 13k literature-mined fracture surfaces

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Vision-language models (VLMs) have shown strong potential for scientific image understanding, but general-purpose models often lack the domain-specific visual knowledge required for reliable materials characterization. In this work, we fine-tuned an open-source VLM (Qwen3-VL-32B-Instruct) for fracture-surface image analysis using a curated dataset of 13,168 open-source, literature-mined fracture-surface images. Morphology annotations were generated by GPT-5.2-Reasoning (high) from both the images and relevant excerpts of their source papers, and the dataset was further enriched with targeted manual collection and rotation-based augmentation. The resulting specialist model outperforms flagship proprietary multimodal models on a benchmark of 100 manually annotated images. It achieves a precision of 0.92, compared to 0.35 for the base Qwen3-VL-32B-Instruct, 0.58 for GPT-5.5-Reasoning (high), and 0.78 for Gemini 3.1 Pro-Reasoning (high). Dataset ablations show that manual collection of rare-feature images and augmentation via image rotation are both beneficial to improve recognition of less common fracture morphology features. We further discuss integrated use of the fine-tuned model with proprietary models to combine fracture-specific visual accuracy with broader multimodal reasoning for autonomous fractography. Although focused on fracture-surface images, this work demonstrates how VLMs can be adapted through targeted collection and fine-tuning on novel feature images to recognize those features and support downstream decision-making in autonomous microscopy workflows.
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cond-mat.mtrl-sci 2026-05-08 2 theorems

Model generates crystals invariant to all layer groups

SLayerGen: a Crystal Generative Model for all Space and Layer Groups

SLayerGen improves de-novo creation of diperiodic materials such as thin films by enforcing any of the 80 layer symmetries.

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Crystal generative models have shown rapid progress for accelerating the discovery of bulk, periodic materials. However, many material systems such as 2D superconductors, thin film semiconductors, and catalytic surfaces are diperiodic, i.e., aperiodic along one of the lattice directions. These systems are invariant under the layer groups, which are known to influence materials properties yet not considered by existing models. In this paper, we propose SLayerGen, a generative model that produces crystals constrained to be invariant to any space or layer group. SLayerGen consists of coarse-to-fine discrete autoregressive lattice generation; transformer-based autoregressive sampling of Wyckoff positions, elements, and numbers of symmetrically unique atoms; and space or layer group equivariant diffusion of atomic coordinates. For the diffusion component, we corrected an inconsistency in the loss from prior work arising from hexagonal groups being non-orthogonal in fractional coordinates. To facilitate progress in generative modeling of diperiodic materials, we assembled and filtered datasets of monolayers and bilayers, propose relevant evaluation metrics, and developed novel representations for layer group symmetries. For de novo generation of diperiodic materials, SLayerGen achieves consistent performance gains over bulk crystal generative models and is competitive when training jointly on bulk and diperiodic materials.
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cond-mat.mtrl-sci 2026-05-08 Recognition

Electrode swap alone tunes clay nanofluidic memristor

Two-dimensional Clay Channels for Tunable Nanofluidic Memristor

Asymmetrical vermiculite channels switch between distinct memory loops via polarity without changing electrolyte or structure.

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Dynamic reconfiguration of charge carriers in confined ion-channels under electrical stimulation produces memory effects, where the internal resistance depends on history of the electric field. Vermiculite nanofluidic devices harness this effect to store and process information within a single component. We report switching between distinct memory loops by tuning ion transport pathways, governed by asymmetrical device architecture and intrinsic surface-charge. Polarity-dependent memory switching between crossing-1 and crossing-2 loops is achieved solely by altering electrode configurations, without modifying electrolyte, channel surface chemistry or device structure: providing mechanistic insights into ionic memristors through a straightforward, experimentally validated strategy. The memristive characteristics are demonstrated in both in-plane and out-of-plane channel configurations with channel lengths spanning from centimeters to micrometers length scales using re-stacked vermiculite membranes and further investigated for miniaturization with devices having nanometer scale channel lengths, fabricated via ultramicrotomy method. Furthermore, we demonstrate neuromorphic functionalities, including synaptic potentiation-depression and programmable memory retention, highlighting potential for bio-inspired computing systems. Cost-effective and scalable fabrication solution processed vermiculite membrane memristors pave the way for practical integration of nanofluidic memristors for neuromorphic computing applications.
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cond-mat.mtrl-sci 2026-05-08 2 theorems

Five seed measurements yield domain-wall growth laws

LLM-Guided Open Hypothesis Learning from Autonomous Scanning Probe Microscopy Experiments

Symbolic regression plus LLM ranking evolves incomplete expressions into interpretable voltage-time relations for PZT switching.

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Autonomous experimentation has transformed microscopy and materials discovery by enabling closed-loop optimization including imaging and spectroscopy tuning, strucutre property relationship discovery, and exploration of combinatorial libraries. However, most current workflows remain limited to selecting measurements within fixed objective or hypothesis spaces, rather than generating new physical models from experimental data. Here, we introduce an open hypothesis-learning framework that combines symbolic regression with large-language-model-based physical evaluation and implement it for autonomous scanning probe microscopy. Symbolic regression generates candidate analytical relationships directly from sparse measurements, while the language-model evaluator ranks these candidates according to physical plausibility, scaling behavior, and consistency with known mechanisms. We demonstrate the approach on autonomous piezoresponse force microscopy measurements of ferroelectric domain switching in a PZT thin film. Starting from five seed measurements, the workflow evolves from physically incomplete candidate expressions toward interpretable voltage-time growth laws consistent with kinetic domain-wall motion. This work extends autonomous microscopy from closed-loop optimization toward open hypothesis discovery, where candidate physical laws emerge from the experiment itself rather than being specified in advance. More broadly, the framework establishes a route for integrating symbolic regression, physical reasoning, and adaptive experimentation into hierarchical autonomous scientific workflows.
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cond-mat.mtrl-sci 2026-05-08 2 theorems

Moiré fringes estimate strain in GaAs-(Pb,Sn)Te nanowires

Moire based strain analysis in wurtzite GaAs -- rock-salt (Pb,Sn)Te core-shell nanowires grown by molecular beam epitaxy

Lattice mismatch patterns observed at the core-shell interface provide an alternative way to measure strain in topological insulator shells.

abstract click to expand
We investigate core/shell GaAs/(Pb,Sn)Te nanowire nanoheterostructures with wurtzite (wz) GaAs cores and (Pb,Sn)Te topological crystalline insulator shells. The nanostructures have been grown by molecular beam epitaxy using two distinct MBE systems dedicated to III-V, and IV-VI semiconductors. The interface structure of wz-GaAs/(Pb,Sn)Te nanowires is investigated using high resolution transmission electron microscopy, scanning transmission electron microscopy and geometric phase analysis. Misfit dislocations and moir\'e fringes are observed as a direct result of the lattice mismatch between the core and the shell materials, and used to estimate strain in crystalline topological insulator shells. Our results point to a possibility of using moir\'e patterns analysis as an alternative, for estimating strain in the core-shell nanowire structures.
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cond-mat.mtrl-sci 2026-05-08

Moiré fringes estimate strain in GaAs/PbSnTe nanowires

Moire based strain analysis in wurtzite GaAs -- rock-salt (Pb,Sn)Te core-shell nanowires grown by molecular beam epitaxy

Lattice mismatch produces visible interference patterns that can be read to quantify shell strain without additional specialized tools.

abstract click to expand
We investigate core/shell GaAs/(Pb,Sn)Te nanowire nanoheterostructures with wurtzite (wz) GaAs cores and (Pb,Sn)Te topological crystalline insulator shells. The nanostructures have been grown by molecular beam epitaxy using two distinct MBE systems dedicated to III-V, and IV-VI semiconductors. The interface structure of wz-GaAs/(Pb,Sn)Te nanowires is investigated using high resolution transmission electron microscopy, scanning transmission electron microscopy and geometric phase analysis. Misfit dislocations and moir\'e fringes are observed as a direct result of the lattice mismatch between the core and the shell materials, and used to estimate strain in crystalline topological insulator shells. Our results point to a possibility of using moir\'e patterns analysis as an alternative, for estimating strain in the core-shell nanowire structures.
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cond-mat.mtrl-sci 2026-05-08

Extended defects soften 3C-SiC stiffness by up to 6%

Molecular dynamics simulation study of mechanical properties of 3C-SiC with extended defects

Simulations with two potentials show Shockley partials and dislocation complexes lower average elastic moduli in cubic silicon carbide.

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In this study, large-scale molecular dynamics simulations with the Vashishta potential and the analytic bond-order potential (ABOP) were performed to investigate the effect of extended defects on the elastic properties of cubic silicon carbide (3C-SiC). Specifically, we focused on systems containing Shockley partial dislocations terminating stacking faults, along with double and triple dislocation complexes. The changes in the independent elastic stiffness constants C11, C12 and C44 upon varying the mentioned extended defects concentrations were quantified. Using the values of these constants, the effective bulk, shear, and Young's moduli were calculated for different defect types and concentrations. The moduli were calculated along particular crystallographic directions aligned with the mentioned defect configurations as well as evaluated using Voigt-Reuss-Hill averaging to provide overall orientation-independent characterization of the defect-altered lattice. The obtained results reveal a general trend of diminishing the material's stiffness with increasing densities of Shockley partial dislocations and dislocation complexes. Depending on the defect configuration, the average elastic moduli decrease by up to approximately 6 % with the Vashishta potential and up to about 4 % using the analytic bond-order potential. At this, triple dislocation complexes induce smaller perturbations. These findings demonstrate that extended defect networks can measurably modify the elastic response of 3C-SiC and should be considered in further scientific research and practical applications of this material.
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cond-mat.mtrl-sci 2026-05-08

Monohydride bending mode on (111) faces drives Fano resonance in nanodiamond IR spectra

On Fano effect in IR spectra of hydrogenated nanodiamonds

Size-dependent analysis rules out C-H stretches of adsorbed groups and points instead to coupling with the diamond optical phonon.

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Hydrogenated nanodiamonds may show a "transmission window" in infra-red spectra in the vicinity of diamond Raman frequency. This phenomenon is a manifestation of resonance coupling of incident photons with continuum states (Fano resonance). Hpwever, precise mechanism of appearence of the resonance and of related conductivity - surface hydrogenation or specific type of surface reconstruction - remains debatable. We present detailed analysis of infra-red spectra of nanodiamonds of different sizes (2.6-30 nm) possessing the "transmission window" and show that the C-H stretch vibrations of adsorbed functional groups cannot be responsible the the Fano resonance. At the same time, it is suggested that a bending mode of monohydride termination on nanodiamond (111) face may couple with diamond optical phonon, explaining the Fano resonance in some cases. The relative importance of the monohydride contribution and of the graphitic islets to the appearence of the "transmission window" and conductivity is likely dependent on dominating morphology and size distribution of nanodiamond grains.
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cond-mat.mtrl-sci 2026-05-08 Recognition

Ternary blends push RAINBOW cells to 17.3% efficiency

Exploring the Potential of Ternary Blending for Two and Three-Junction RAINBOW Solar Cells

Side-by-side three-junction organic devices outperform single-junction cells by more than 4 points using scalable blade coating.

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The efficiency of organic photovoltaics (OPV) has been steadily increasing over the past decade until reaching the 20\% milestone. Multijunction architectures provide a promising approach to further enhance performance. Here we explore the potential of a spectral splitting geometry, referred to as RAINBOW, in which subcells are placed side-by-side and externally connected, thus minimizing the fabrication and current matching challenges found in vertically stacked configurations. First, we tested 7 different binaries with bandgaps spanning from 1.98 to 1.16 eV. The systems with the widest and narrowest gaps suffered greater losses and so we evaluate if ternary mixing could help to overcome these limitations by evaluating 5 different ternaries. Generally speaking, ternary mixing tunes the Voc, and when morphology and energy levels are well aligned, the overall PCE can be boosted in the spectral region where the subcell should absorb, as is the case for PTB7-Th:COTIC-4F:BTP-eC9 when operating as red subcell. Device simulations help to identify the 2-junction and 3-junction configurations with highest PCEs, all of which include ternaries. We fabricate proof-of-concept RAINBOW devices using scalable methods in which the subcells are deposited by meniscus-guided blade coating. The efficiency improves from 12.9\% in single-junction devices to 15.9\% in 2-junction devices (16.4\% in simulations) and 17.3\% in 3-junction devices (17.7\% in simulations), confirming the viability of the RAINBOW architecture for scalable, high-efficiency OPVs. Finally, detailed balance analysis indicates that the potential of this geometry can be very high provided that high efficiency wide bandgap (2-2.5eV) materials become available.
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cond-mat.mtrl-sci 2026-05-08

Low sputter pressure raises HER activity in platinum films through strain

From Deposition Stress to Surface Reactivity: Strain-Dependent Hydrogen Evolution on Sputtered Platinum Thin Films

Dense low-pressure deposits outperform rough high-pressure films because compressive strain improves hydrogen binding despite smaller area.

abstract click to expand
Strain has emerged as a promising approach for tuning electrocatalytic properties, yet its role in sputter-deposited thin films remains poorly understood. In this work, magnetron-sputtered platinum (Pt) thin films with different stress states were prepared by varying the sputter pressure. The resulting changes in microstructure, residual strain, and hydrogen evolution reaction (HER) activity were investigated using complementary characterization techniques and density functional theory (DFT) calculations. Structural analysis reveals a transition of (111)-textured Pt thin films from dense and smooth films at low pressures, to more porous microstructures with increased roughness at higher pressures. Electrochemical measurements show that films deposited at low sputter pressure exhibit the highest HER activity, while higher sputter pressures lead to reduced activity despite increased surface area. DFT calculations demonstrate that lattice strain alters hydrogen adsorption energetics and surface coverage on Pt(111), providing a mechanistic explanation for the observed activity trends. Overall, the results highlight that HER activity in sputtered Pt thin films is governed by the interplay of residual strain, microstructure, and hydrogen coverage.
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cond-mat.mtrl-sci 2026-05-08

Neutron scattering shows magnons winding around K in CrI3

Winding feature and thermal evolution of the Dirac magnons in CrI₃

Data map the Dirac signature in the 2D ferromagnet and its T squared energy shift from magnon scattering.

Figure from the paper full image
abstract click to expand
Two-dimensional honeycomb lattice ferromagnet chromium tri-iodide (CrI$_3$) has attracted tremendous interest because it retains ferromagnetism down to the monolayer limit and hosts intriguing topological magnons. As a prototypical van der Waals magnet, CrI$_3$ provides an ideal platform for exploring the interplay between reduced dimensionality, magnetic order, and nontrivial spin excitations. Here, using inelastic neutron scattering together with improved sample quality, we uncover the magnon winding feature around the $K$-point of the hexagonal Brillouin zone, a key signature of Dirac magnons. In addition, we find that the magnon energy follows a $T^2$-renormalization behavior at elevated temperatures, consistent with magnon-magnon interactions. These results provide previously missing information on the magnon spectrum of CrI$_3$ and further consolidate the topological nature of its spin excitations.
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cond-mat.mtrl-sci 2026-05-08

Magnetic fields tune domains in Mn3NiN but not Mn3GaN

Disentangling magnetic and optical contributions in ultrafast dynamics of antiperovskite non-collinear antiferromagnets

Polarization scans and optical modeling isolate piezomagnetic domain shifts from non-magnetic signals in these antiperovskite films.

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Non-collinear antiferromagnets are a class of spin-polarized antiferromagnets in which chiral spin textures give rise to Berry-curvature-driven phenomena, such as the anomalous Hall effect (AHE), without net magnetization. We investigate the properties of thin films of antiperovskite non-collinear antiferromagnetic metals Mn3NiN and Mn3GaN using pump-probe experiments. In both materials, we observe a strong dependence of pump-polarization-independent dynamics, induced by femtosecond laser pulses, on the angle between the sample normal and the direction of probe propagation. In Mn3NiN, where the presence of a sizable AHE indicates the {\Gamma}4g phase, the measured magnetooptical (MO) signals acquire an additional, strong dependence on the external magnetic field when the probe pulses are incident at nonzero angles. In contrast, in Mn3GaN, where the absence of AHE indicates the {\Gamma}5g phase, the measured signals do not depend on the magnetic field. Using probe-polarization-resolved measurements combined with full optical modeling based on Yeh's formalism, we quantitatively separate magnetic and non-magnetic contributions to the measured signals. We show that in Mn3NiN, the observed magnetic field dependence results from field-controlled redistribution of magnetic domain populations, enabled by their piezomagnetic moments and detected by a Kerr-like MO effect, while this effect is absent in Mn3GaN. Temperature-dependent measurements reveal a change from single-step to two-step quenching dynamics with increasing temperature in Mn3NiN. This behavior contrasts with the nearly temperature-independent quenching dynamics reported for the non-collinear antiferromagnetic Heusler compound Mn3Sn, but resembles the crossover from type-I to type-II demagnetization dynamics in metallic ferromagnets.
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cond-mat.mtrl-sci 2026-05-08

Reduction turns polyynes into stable sp-sp2 nanoparticles

Charge-Transfer Induced Reactivity in sp Carbon Atomic Wires: Towards 0-D sp-sp2 Nanostructures

The particles keep over 60 percent sp character, show tunable sizes, and remain intact in air for more than six months.

Figure from the paper full image
abstract click to expand
Carbon Atomic Wires (CAWs) are finite linear chains of sp-hybridized carbon atoms. Here the electrochemical reduction of CAWs in the form of polyynes (i.e. with alternated single-triple bonds) is reported. Upon applying a reducing potential to a solution containing polydispersed hydrogen-capped polyynes, the formation of a black precipitate was observed. Electronic absorption spectroscopy confirmed the irreversible reaction of the carbon chains while excluding degradation or side reactions. Subsequent analyses revealed that the precipitate consisted of amorphous carbon nanoparticles with tunable diameters. This control over particle size is attributed to the modulation of growth kinetics through restricted mass transport toward the solid-liquid interface. Raman spectroscopy showed that the resulting material exhibits an amorphous sp-sp2 character, with a retained sp fraction exceeding 60%. Smaller nanoparticles displayed reduced disorder within the sp2 domains and a broader distribution of sp-chain lengths preserved in the amorphous matrix. Additional experiments on size-selected polyynes suggest that this synthesis method allows to better preserve the starting chain length in the final structure. Unlike previously reported amorphous sp-sp2 carbon networks, the nanoparticles produced in this study show remarkable stability under ambient conditions, retaining their sp character for times in excess of six months. These findings pave the way for future applications, particularly as further diameter tuning may enable access to the quantum-dot regime.
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cond-mat.mtrl-sci 2026-05-08

Pressure suppresses shear twinning in BCC nanocrystals

Transformation-mediated twinning governs plasticity in body-centered cubic nanocrystals under extreme loading

Compression instead triggers dual-shuffle via HCP phases in moderate-stiffness materials like Fe, Ta and Nb.

abstract click to expand
Plasticity in body-centered cubic (BCC) nanocrystals is often associated with twin nucleation phenomena under extreme loading conditions. Here, we reveal unconventional twinning pathways that operate at the intersection of crystal plasticity and structural phase transitions. We show that the classical shear-driven twinning mode becomes progressively suppressed with increasing pressure, giving rise to transformation-mediated twinning pathways involving transient HCP or FCC phases. In BCC Fe, Ta, and Nb nanocrystals of moderate elastic stiffness, plasticity is consistently initiated by an elastic instability that triggers a dual-shuffle process mediated by stable or metastable hexagonal closed-packed (HCP) phases. This pathway operates independently of the characteristic {112} twin boundary planes and is driven by compression, challenging the conceptual paradigm for metal plasticity in which plastic deformation arises from shear stresses resolved on specific planes. By contrast, in the archetypal elastically stiffer BCC Mo and W nanocrystals, plastic deformation proceeds via two alternative twinning pathways associated with shear-driven elastic instabilities mediated by highly-distorted face-centered cubic (FCC) phases. Comprehensive analyses of the energy landscapes to the competing nanoscale twinning modes provide mechanistic insight into their activation, establishing a unified framework for transformation-mediated twinning in BCC nanocrystals across a broad range of loading conditions.
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