cond-mat.mes-hall

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cond-mat.mes-hall 2026-05-14 2 theorems

MoSe2/PdSe2 stack lifts A-exciton emission sixfold

Highly Efficient Exciton Modulation in MoSe₂/PdSe₂ Heterostructures

Interlayer coupling redirects excitons to raise room-temperature quantum yield from 1% to 6% without strain or doping.

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Controlling exciton recombination in atomically thin semiconductors is central to their optoelectronic functionality, as the competition between radiative and non-radiative decay channels governs emission efficiency. Existing approaches, such as defect passivation, chemical doping, dielectric engineering, and strain tuning, primarily aim to suppress non-radiative losses. Here, we report a pronounced $\sim$6-fold enhancement of room-temperature A-exciton emission in a type-I MoSe$_2$/PdSe$_2$ van der Waals heterostructure, yielding a photoluminescence quantum yield of 6 %, compared to $\sim$1 % for as-exfoliated monolayer MoSe$_2$. This enhancement is accompanied by strong quenching of the B-exciton, consistent with interlayer electronic coupling that redistributes exciton populations toward the radiative A-exciton channel. Power- and temperature-dependent measurements reveal a suppression of exciton-exciton annihilation and a crossover to quenched emission at low temperature, indicating a redistribution of exciton relaxation pathways. Photoluminescence excitation spectroscopy further reveals a broadband enhancement spanning 450-725 nm, ruling out a resonance-specific mechanism. These results demonstrate that interlayer electronic coupling can be used as an efficient means to redirect exciton populations toward radiative channels, enhancing emission efficiency in two-dimensional semiconductors without chemical modification or strain.

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cond-mat.mes-hall 2026-05-14

Floquet systems quantize conductance to winding number via sideband sum

Quantized Transport in Floquet Topological Insulators

Numerical and analytic results show both longitudinal and Hall conductances reach exact multiples of e²/h only after all replica bands are,

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We study quantum transport in a periodically driven (Floquet) topological system coupled to static fermionic reservoirs. Using the Floquet nonequilibrium Green's-function (NEGF) formalism we show, from exact numerics for a strip geometry, that the two-terminal (longitudinal) conductance is quantized as $|W_{\varepsilon}|\,e^2/h$, while the Hall (transverse) conductance is quantized as $W_{\varepsilon}\,e^2/h$, where $W_{\varepsilon}$ is the Floquet winding invariant associated with the quasienergy gap at $\varepsilon = 0$ or $\varepsilon = \Omega/2$. Quantization is achieved only after summing over the contribution of all Floquet sidebands. We provide an analytic understanding of this Floquet conductance sum rule, by considering the Hall conductance in the weak coupling limit. In that limit, we show that the Floquet Hall conductance gets contributions from the Floquet sidebands, which includes the signs of the velocities of the edge modes. Their sum yields exact quantization, as predicted by the Floquet sum rule. We find that in a wide range of parameter regime, the convergence is fast, making observation of the sum rule and Floquet winding numbers accessible to experiments.

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cond-mat.mes-hall 2026-05-13 Recognition

Screw dislocation splits optical shifts in GaAs quantum wire

Optical Response of a screw dislocated GaAs Quantum Wire: Temperature and Pressure Effects

The dislocation parameter redshifts one transition while blueshifting the other; temperature and pressure further tune positions and heights

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We investigate the influence of a screw dislocation, characterized by the dislocation parameter, on the optical response of a parabolic GaAs cylindrical quantum wire under the combined effects of temperature, hydrostatic pressure, and the axial magnetic field. Using a torsion-modified metric together with pressure- and temperature-dependent material properties, namely the effective mass and dielectric permittivity, we obtain exact solutions of the Schr\"odinger equation in terms of Whittaker functions. The screw dislocation introduces a $k_z$-dependent coupling that breaks the symmetry between the angular momentum states $m$ and $-m$ and modifies the centrifugal term in the effective potential. Based on the resulting eigenstates, we evaluate the linear and third-order nonlinear optical absorption coefficients, as well as the corresponding refractive index changes, for the dipole-allowed transitions $m = 0 \to +1$ and $m = 0 \to -1$. Our results show that increasing the dislocation parameter produces a pronounced redshift and suppresses the resonance amplitude for the $m = 0 \to +1$ transition, whereas the $m = 0 \to -1$ transition exhibits a blueshift accompanied by peak enhancement. We further find that increasing temperature shifts the resonances toward higher photon energies and enhances their amplitudes, while hydrostatic pressure causes a redshift and reduces the peak intensity for both transitions. In addition, the magnetic field strengthens the optical response and induces a blueshift for the $m = 0 \to +1$ transition, whereas the opposite behavior is obtained for the $m = 0 \to -1$ transition. We have also examined the behavior of the refractive index changes, which exhibit analogous asymmetric dependence on the dislocation parameter.

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cond-mat.mes-hall 2026-05-13 1 theorem

Magnon polaritons form in 30-nm Cr2Ge2Te6 flakes

Magnon polaritons in a van der Waals ferromagnet coupled to a superconducting resonator

Coupling to a superconducting resonator produces avoided crossings whose strength scales with the square root of thickness.

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Achieving magnon-photon hybridization in the microwave regime is essential for integrating magnetic excitations with superconducting circuits. While this has been extensively demonstrated in bulk magnetic systems, realizing it in two-dimensional van der Waals materials remains challenging due to their reduced magnetic volume and increased dissipation. Here, magnon-photon hybridization is observed in exfoliated flakes of the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$, with thicknesses down to 30 nm. The resulting magnon polaritons-hybrid excitations of cavity photons and magnons-are evidenced by reproducible avoided crossings across six devices, enabled by a low-impedance superconducting resonator design. The coupling strength follows the expected square-root dependence on thickness, and extrapolation of this scaling indicates that hybridization in the monolayer limit is within reach.

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cond-mat.mes-hall 2026-05-13 Recognition

Bilayer graphene dots show 0.5-0.9 neV/√Hz charge noise

Probing charge noise in bilayer graphene quantum dots by Landau-Zener-St\"uckelberg-Majorana spectroscopy

LZSM spectroscopy finds thermal or phonon sources dominate over two-level fluctuators and match silicon and III-V levels.

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Charge noise is an important factor limiting qubit coherence and relaxation in solid-state devices. In bilayer graphene (BLG) quantum dots, recently established as a promising platform for spin- and valley-based qubits, both the origin and magnitude of charge noise remain largely unexplored. Here, we investigate high-frequency charge noise using Landau-Zener-St\"uckelberg-Majorana (LZSM) interference spectroscopy. We study a single-particle charge qubit formed in a BLG double quantum dot at frequencies between 5 and 10 GHz and extract a noise spectral density $S_\varepsilon$ on the order of 0.5-0.9 neV$/\sqrt{\mathrm{Hz}}$. This is comparable to values reported for III-V semiconductor platforms and silicon. From the temperature and frequency dependence of the charge qubit decoherence, we conclude that thermal (Johnson) noise or electron-phonon coupling dominates over two-level fluctuators.

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cond-mat.mes-hall 2026-05-13 2 theorems

Bistable flows in electron fluid yield S-shaped I-V curves

Flow bistability in non-Newtonian electron fluid

Two coexisting steady states in narrow channels of non-Newtonian 2D conductors produce voltage-dependent current switching and hysteresis.

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Modern two dimensional conductors with low defect densities and strong electron-electron scattering are favorable platforms for formation of a viscous fluid of conduction electrons. Electric properties of these systems are determined by the hydrodynamic regime of charge transport distinguished by many experimental signatures: a decrease in sample resistance with increasing temperature (the Ghurzhi effect), strong negative magnetoresistance and others. Here we consider the flow of 2D electron fluid in the nonlinear regime characterized by non-Newtonian viscosity which depends on spatial gradients of hydrodynamic velocity. We derive a simplified version of the dynamic equations for the non-Newtonian electron fluid and consider the specific underlying mechanism associated with local electron heating. Recent works have demonstrated that this may be one of the main mechanisms for nonlinearity in 2D electron fluids. We show that in a certain range of parameters, the two steady-state flow configurations coexist for the narrow channel geometry, and this bistability leads to an S-shaped current-voltage characteristic. By solving the derived time-dependent dynamic equations, we trace the transient response to a step variation of the longitudinal voltage and demonstrate how the current switching and hysteresis occur in samples with the non-Newtonian electron fluid.

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cond-mat.mes-hall 2026-05-13 1 theorem

Edge states appear in hexagonal chains below critical hopping ratio

Topological edge states of the hexagonal linear chain

The topological phase of the one-dimensional model produces exponentially localized boundary states only when one hopping amplitude is the

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We study the eigenspectrum properties of a one-dimensional molecular chain composed of hexagonal unit cells. The system features two alternating hopping parameters, resulting in a rich energy spectrum with both dispersive and flat bands. By analyzing the model under periodic and open boundary conditions, we identify two insulating phases separated by a gap-closing transition controlled by the ratio of hopping amplitudes. In the topological phase, realized when the hopping ratio falls below a critical value, edge states emerge that are exponentially localized at the boundaries of finite chains.

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cond-mat.mes-hall 2026-05-13 2 theorems

Laser sidebands suppress WSe2 barrier tunneling

Laser-assisted tunneling in a static tungsten diselenide WSe₂ barrier

Floquet interference and energy shifts overcome Klein tunneling and enable dynamic transport control.

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We study the tunneling effect of Dirac fermions in a monolayer WSe$_2$ subjected to a static electrostatic barrier and irradiated by a linearly polarized laser field. Within the Floquet formalism, the time-periodic driving is incorporated to derive analytical wave functions across the three regions of the system. By enforcing continuity conditions at the interfaces, we obtain the transmission and reflection coefficients, which are then used to evaluate the conductance via the B\"uttiker approach. Our results reveal that the laser field induces a rich Floquet sideband structure, whose number and strength increase with the driving parameter $\alpha$. This leads to a significant suppression of transmission and provides an efficient mechanism to overcome Klein tunneling. Moreover, increasing the width of the irradiated region enhances the interaction between fermions and the external field, resulting in energy renormalization and the formation of Stark-like confined states. The interaction between several Floquet channels creates strong interference effects, which reduce the transmitted current even further. The results demonstrate that light-matter interaction allows for the dynamic control of quantum transport in WSe$_2$ materials. This technology allows for the development of new optoelectronic devices, including tunable quantum filters and light-controlled nanoscale transistors.

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cond-mat.mes-hall 2026-05-13 2 theorems

Free fermion classification reduces to graded algebra decomposition

The Algebra of Free Fermions: Classifying Spaces, Hamiltonians, and Computation

Encoding symmetries in a Z2-graded algebra turns the problem into a representation extension that yields both classification and explicit 0D

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Research on topological phases of matter is a core field in modern condensed matter physics. Free fermion systems, such as topological insulators and superconductors, have been studied using the "Tenfold Way" and K-theory. Building on Kitaev's idea of $\Omega$-spectrum and classifying space, as well as Freed-Moore's K-theory, this work demonstrates that free fermionic systems form a genuine $G$-$\Omega$-spectrum and clarifies its connection to several distinct classification schemes appearing in the physical literature. By introducing the $\mathbb{Z}_2$-graded algebra $A_{\mathrm{sym}}^V$, the classification problem for systems with general symmetries, including antilinear symmetries, antisymmetries, projective representations, and point group symmetries, is turned into an extension problem in representation theory. To solve this, a computational method for the $\mathbb{Z}_2$-graded Wedderburn-Artin decomposition of $A_{\mathrm{sym}}^V$ is developed. This decomposition not only yields a classification but also enables the explicit construction of the corresponding Dirac Hamiltonian. Furthermore, a GAP programming package has been developed to automate these calculations.

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cond-mat.mes-hall 2026-05-12 2 theorems

Antiferromagnetism emerges in MoSe2 quantum Hall states

Optical signatures of antiferromagnetic correlations in a strongly interacting quantum Hall MoSe2 monolayer

Valley Landau level crossings broaden at low fillings, revealing interactions that favor an unpolarized ground state over conventional ferom

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Strong magnetic fields quench the kinetic energy of electrons, leading to the formation of flat energy bands, known as Landau levels (LLs). In this situation, even weak interactions can drive the emergence of various ordered phases. The simplest of such phases is a quantum Hall ferromagnet, where a spontaneous spin polarization emerges when LLs with opposite spins cross. The presence of strong electron-electron interaction at zero field changes this picture and makes the resulting states much harder to predict. Here we use magneto-optical spectroscopy to reveal quantum Hall states with unconventional correlations favouring an unpolarized state in the strongly correlated electron liquid in a MoSe2 monolayer. The oscillations of the exciton polaron energies as a function of perpendicular magnetic field and electron density demonstrate the emergence of LLs in a correlated electron liquid and density-dependent crossings between LLs of opposite valleys. On lowering the LL filling factor, where interactions within LLs are stronger, the crossings systematically broaden, indicating an increase in the Zeeman energy required to fully polarize the valley-degenerate LLs. These observations are shown to be consistent with antiferromagnetic interactions between LL electrons, favouring a ground state with zero valley polarization, and are therefore inconsistent with conventional quantum Hall ferromagnetism. This discovery demonstrates a qualitatively distinct form of quantum Hall magnetism in a strongly correlated electron liquid, establishing an anchoring point for understanding spin-unpolarized fractional and ordered states of correlated electrons driven by magnetic field.

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cond-mat.mes-hall 2026-05-12 2 theorems

Magnetic field induces tunable hyperbolic polaritons in semimetals

Magnetic-field-tunable cyclotron hyperbolic polaritons

Cyclotron motion creates dielectric anisotropy below resonance that supports field-controlled modes observable by terahertz imaging.

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Hyperbolic polaritons are conventionally associated with structural anisotropy or phononic Reststrahlen bands. Here, we predict a new class of hyperbolic polaritons arising from magnetic-field-induced cyclotron motion of charge carriers. When a perpendicular magnetic field is applied to high-mobility semimetals, the cyclotron response drives the in-plane dielectric function from metallic- to insulating-like below the cyclotron resonance frequency, while the out-of-plane response remains metallic. This anisotropy creates a hyperbolic dielectric environment that supports field-tunable hyperbolic polaritons. We develop a comprehensive theoretical framework incorporating coupling to other collective excitations and show that these modes can be directly visualized in real space via terahertz near-field nanoscopy. Our work identifies cyclotron motion as a new route to hyperbolic polaritons and establishes a versatile platform for magnetically programmable nanophotonics.

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cond-mat.mes-hall 2026-05-12 2 theorems

Zigzag edges define four classes of graphitic quadrupole insulators

Bound States in Second-order Topological Graphitic Structures

Domain intersections produce protected massless corner states; smoother walls add massive states with angular momentum.

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Quadrupole insulators are a class of second-order topological insulators (SOTIs) that host zero-dimensional corner states within a two-dimensional bulk. Despite their unique properties, their realization in electronic systems on realistic material platforms remains rare. In this work, we present a general design principle to obtain quadrupole insulators based on two-dimensional graphitic structures. By engineering the positions and connections of zigzag edges, we identify four topological classes of graphitic structures. We show that topologically protected massless corner state emerge at the intersection of domains belonging to different topological classes. Crucially, by tuning the smoothness of the domain wall, we further demonstrate the appearance of additional massive localized states with non-zero angular momentum. Our results provide a practical framework for realizing experimentally accessible SOTIs and uncover the coexistence of both massless and massive bound states in two dimensions.

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cond-mat.mes-hall 2026-05-12 1 theorem

Photon momentum breaks symmetry to enable bulk photocurrents in PdTe

Photon Momentum Enabled Symmetry Breaking and Nonlinear Photocurrents in the Centrosymmetric Dirac Semimetal PdTe

Thickness-dependent measurements show the helicity-dependent response originates in the centrosymmetric bulk rather than surfaces.

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In centrosymmetric Dirac semimetals, second order nonlinear photocurrents are forbidden by the coexistence of time-reversal and inversion symmetries. Here, we demonstrate that finite photon momentum transfer acts as a dynamic symmetry breaking mechanism in PdTe, enabling nonlinear optical responses that are nominally forbidden in the centrosymmetric bulk. Through polarization sensitive measurements, we resolve distinct contributions from the circular photogalvanic effect (CPGE), geometric shift currents, and photon drag mediated processes. We show that the helicity dependent current vanishes at normal incidence and reverses sign with the angle of incidence, reflecting the coupling between photons and spin polarized surface states. Crucially, thickness dependent analysis reveals that the helicity dependent photocurrent component C scales with film thickness, establishing a robust bulk contribution enabled by momentum transfer. This confirms that incident photons provide the directional axis required to probe interband quantum geometry, rather than the response originating solely from surface states or strain. Our results demonstrate that optical excitation can dynamically reduce the effective symmetry of the system, enabling access to quantum geometric tensors and establishing PdTe as a promising platform for exploring nonequilibrium dynamics governed by photon momentum in high symmetry topological materials.

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cond-mat.mes-hall 2026-05-12 1 theorem

Valley splitting tunes Dirac fluid viscosity nonmonotonically

Valley-Controlled Viscosity of Two-Dimensional Dirac Fluids

Shifting Dirac cones in twisted bilayer graphene drives the system through depletion, neutrality crossover, and electron-hole scattering, re

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Motivated by recent experiments in weakly hybridized small-angle twisted bilayer graphene, we investigate how valley imbalance affects the viscosity of two-dimensional Dirac fluids. We show that shifting the two low-energy Dirac cones relative to one another provides a direct knob to control the viscosity of the electron fluid. As the splitting is increased, the system passes through distinct transport regimes associated with valley depletion, charge-neutrality crossover, and the onset of electron-hole scattering, producing a pronounced nonmonotonic response. To place this result in context, we also analyze the viscosity in monolayer graphene (MLG) and two-dimensional electron gas (2DEG). We show that, due to the strong dependence of its inertial mass density on temperature, the kinematic viscosity of MLG is a monotonically decreasing function of temperature. Our results identify valley control as a route to tuning hydrodynamic transport in Dirac materials and clarify the interplay between band structure, scattering phase space, and screening in setting the viscous response.

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cond-mat.mes-hall 2026-05-12 2 theorems

Strain converts Andreev states into Majorana modes in hybrid wires

Strain-controlled crossover between Majorana and Andreev bound states in disordered superconductor-semiconductor heterostructures

Weak nonuniform strain enhances nonlocality to stabilize topological states despite disorder in nanowires and ribbons.

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The unambiguous identification of topological Majorana-bound states (MBSs) in superconducting hybrid systems is hindered by trivial low-energy excitations, especially partially separated Andreev bound states (psABSs), which can mimic Majorana signatures. Here we show that spatially nonuniform strain offers a systematic route to control and interconvert these low-energy states. Using tight-binding Bogoliubov--de Gennes simulations, we study one-dimensional semiconductor nanowires and graphene nanoribbons with superconductivity, Rashba spin-orbit coupling, Zeeman fields, and disorder. We find that even weak strain can qualitatively reshape the low-energy spectrum by modifying effective band parameters and redistributing wavefunction weight. In nanowires, strain tunes the spatial overlap of Majorana components and shifts the topological phase boundary, enabling controlled crossovers between trivial states, psABSs, and topological MBSs. In graphene nanoribbons, where multiband effects and edge states produce a dense, hybridized low-energy spectrum, strain suppresses subband mixing, lifts degeneracies, and stabilizes boundary-localized modes. In both platforms, we identify regimes where disorder-induced psABSs are converted into well-separated and robust MBSs through strain-enhanced nonlocality. We further develop an analytical framework based on a position-dependent topological mass and strain-driven domain-wall motion, which captures the physical mechanism of these crossovers and yields a real-space criterion for the emergence and stability of Majorana modes. Our results establish strain as an effective tuning parameter for distinguishing and stabilizing topological MBSs in realistic disordered systems, and suggest an experimentally relevant pathway toward improved control and identification of Majorana modes in complex hybrid structures relevant to topological quantum computation.

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cond-mat.mes-hall 2026-05-12 2 theorems

Altermagnets produce magnetoresistance tied only to magnetization-Néel angle

Theory of Spin-splitter Magnetoresistance in Altermagnets

The spin-splitter effect yields opposite-sign longitudinal response and proportional signals, unlike conventional spin-Hall magnetoresist

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We develop a theory of angle-dependent magnetoresistance (ADMR) in metallic altermagnets coupled to ferromagnetic insulators and establish criteria that distinguish them from conventional compensated magnets with spin-orbit coupling. We show that the spin-splitter magnetoresistance (SSMR) reported by H. Chen et al. [Adv. Mater. 37, 2507764 (2025)] constitutes a smoking-gun signature of collinear altermagnetism in metallic systems. In contrast to spin-Hall magnetoresistance (SMR), SSMR exhibits three key distinctions: it depends solely on the relative orientation between the ferromagnetic magnetization and the altermagnetic N\'eel vector, yields a longitudinal ADMR response of opposite sign, and features a direct proportionality between longitudinal and transverse ADMR signals, absent in SMR. These results provide a clear route to unambiguously identify altermagnets in transport.

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cond-mat.mes-hall 2026-05-12 Recognition

Altermagnetism inherent in certain hyperbolic lattices

Inherent Altermagnetism on regular hyperbolic lattices

Next-nearest neighbor hopping in tight-binding models on the Poincaré disk produces momentum-dependent spin splitting without net magnetiz

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Altermagnets are a novel class of magnetic systems characterized by their momentum-dependent spin splitting without net magnetization. In this work, we extend established Euclidean tight-binding models of altermagnets to regular hyperbolic lattices in two spatial dimensions defined on a discretized Poincar\'e disk. Using hyperbolic crystallography and hyperbolic band theory, we show that the inclusion of next-nearest neighbor hopping is sufficient to induce spin splitting in bipartite hyperbolic lattices. While certain families and special cases of hyperbolic lattices remain antiferromagnetic, we identify an entire family and a special case that show spin splitting in this framework. Hence, altermagnetism is inherent to certain hyperbolic lattices. Since hyperbolic band theory yields a momentum space that is at least four-dimensional, we classify the leading spin-splitting harmonics using four-dimensional atomic orbitals.

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cond-mat.mes-hall 2026-05-12 3 theorems

Resonance window at 4.9 speeds up quantum gates 9x

Ultra-Fast Quantum Control via Non-Adiabatic Resonance Windows: A 9x Speed-up on 127-Qubit IBM Processors

Experiments on 127-qubit IBM chips find non-adiabatic control that cuts gate time while holding fidelity, but drifts quickly degrade the win

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Standard adiabatic protocols for superconducting qubits often face a trade-off between gate speed and decoherence. In this work, using IBM Quantum 127-qubit processors (ibm_fez and ibm_kingston), we report the discovery of a fundamental non-adiabatic resonance window at about 4.9. This window demonstrates the potential for a 9.2-fold reduction in gate duration relative to the conventional adiabatic limit, while maintaining state high fidelities within the identified resonance windows. Through synchronous cross-backend execution, we demonstrate a near-perfect correlation (R = 0.9998) in the resonance profile, confirming the universality of the non-adiabatic parameter across independent hardware architectures. However, our longitudinal analysis reveals that these high-Q windows are sensitive to sub-percent calibration drifts, which dynamically shift the system into a stochastic regime. These findings suggest that achieving next-tier quantum performance requires a transition from static gate protocols to dynamic resonance-tracking control tools. This study provides both the theoretical foundation and the experimental evidence for such ultra-fast, high-performance quantum architectures.

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cond-mat.mes-hall 2026-05-12 Recognition

Confinement raises critical charge in 1D Dirac atom

One-dimensional relativistic hydrogen-like atom in Dirac materials: Energy spectra and supercritical states

Graphene nanoribbon calculations show the nuclear charge threshold for supercritical states increases under box confinement, accompanied by

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We consider a model of 1D relativistic hydrogen-like atom, formed by a Coulomb impurity in graphene nanoribbon. Describing the electron motion in terms of the one-dimensional Dirac equation for Coulomb potential taking into account the finite-size of the atomic nucleus, we compute the eigenvalues and eigenfunctions of the atomic electron. The cases of unconfined atom and atomin-box system are considered. Special focus is given calculation of supercritical energy levels and the critical charge. The latter is the value of the atomic nucleus charge, when the electronic state reaches the border of the Dirac sea. It is found that for confined atom the value of the critical charge is larger than that of free atom. Experimentally measurable characteristics, local density of states is also plotted for both cases. Existence of strong localization for atom-in-box system is shown.

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cond-mat.mes-hall 2026-05-12 2 theorems

New resistance dips mark states at 17/33 and 15/31

Cascade of fractional quantum Hall states in 2D system

High-mobility GaAs wells reveal additional fractions that fit a composite-fermion pattern ranking their relative strengths.

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The observation of the fractional quantum Hall (FQH) effect in 2D electron gases ushered in investigations of topological phases driven by strong electron correlations. Their remarkable features include fractionalized elementary excitations, gapless boundary states, and non-trivial quantum entanglement patterns. Thanks to persistent efforts in the building of new platforms and making higher-quality samples, a diverse plethora of FQH states have been unveiled in experiments. We report a systematic study of ultrahigh-quality GaAs/AlGaAs quantum wells with mobility up to 3.7*10^7 cm^2/V/s using quantum transport measurements in nuclear adiabatic demagnetization and dilution refrigerators down to 1 mK. In addition to many FQH states that have already been identified in previous work, new longitudinal resistance dips are observed at filling factors 17/33 and 15/31. The application of an in-plane magnetic field causes disparate variations of the FQH states. The theoretical foundation of these states is discussed in the framework of composite fermion theory. While most fractions can be explained as non-interacting composite fermions forming integer quantum Hall states, a few states correspond to FQH states of composite fermions that arise from residual interaction between them. We summarize the observed fractions in the range of 0 < {\nu} < 2 and propose a pattern to account for their experimental appearance that provides an intuitive picture about the relative strengths of different FQH states.

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cond-mat.mes-hall 2026-05-12 Recognition

Temperature gradients drive orbital currents in TMD monolayers

Orbital and Spin Nernst Effects in Monolayers of Transition Metal Dichalcogenides

The orbital Nernst effect arises from Berry curvature without needing spin-orbit coupling, while the spin version requires it and can be tun

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In recent years, orbitronic effects have attracted growing attention as complementary counterparts to the well-established spintronic phenomena. In this work, we demonstrate that monolayers of transition metal dichalcogenides provide an excellent platform for the observation of the orbital Nernst effect, a relatively less explored phenomenon describing the generation of a transverse orbital current in response to an applied temperature gradient. We show that, similar to its electrical counterpart, viz., the orbital Hall effect, the orbital Nernst effect does not require the presence of spin-orbit coupling. Analytical results based on a low-energy valley model offer key insights into the underlying mechanisms, highlighting in particular the crucial role of electronic states at the Fermi energy for the emergence of this effect. The inclusion of spin-orbit coupling further gives rise to a spin Nernst effect, which scales with the strength of spin-orbit coupling and vanishes in its absence. We substantiate our analytical findings with full Brillouin-zone tight-binding results for two representative systems, monolayer 2H MoS$_2$ and 2H NbS$_2$. Our results show that while both orbital and spin Nernst conductivities in MoS$_2$ require electron or hole doping, both effects are intrinsically present in metallic NbS$_2$. Our work reveals the central role of orbital and spin Berry curvatures, identifies doping as an effective route for tuning orbital and spin Nernst responses, and proposes a possible experimental setup for detecting these effects in monolayer transition metal dichalcogenides.

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cond-mat.mes-hall 2026-05-12 Recognition

Hexagonal Hofstadter model yields exact localization phases

Localization phase diagram of the Hexagonal Lattice with irrational magnetic flux

2x2 transfer matrix places nearest-neighbor case inside Avila theory, producing three pure phases with no mobility edge due to chiral symm

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We study the Hofstadter model on a hexagonal lattice with irrational magnetic flux in this work. The Hofstadter model of the square lattice with irrational flux has been solved mathematically by Avila in his Fields medal work. However, this theory is usually not applicable to lattices with internal degrees of freedom, such as spin or sub-lattices. In this work, we show that for the hexagonal lattice with only nearest neighbor hopping, the system can still be characterized by a 2*2 transfer matrix and solved exactly by Avila$'$s global theory of Avila although this lattice has two sub-lattices. We obtained the exact localization phase diagram of the hexagonal lattice with irrational flux by this theory, which reveals three pure phases, that is, the extended, localized and critical states but no mobility edge due to the chiral symmetry. We used the renormalization group (RG) theory to verify these results, which can determine part of the phase diagram. We then computed the fractal dimension of the remaining part numerically. The results from both the RG theory and numerical analysis confirmed the phase diagram we get from Avila$'$s global theory.

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cond-mat.mes-hall 2026-05-12 3 theorems

Geometry-driven gradients produce linear antisymmetric magnetization

Antisymmetric linear transverse magnetization and ferroaxial moments induced by geometry-driven electric field gradients

Finite shapes create electric field gradients that allow a transverse response forbidden by Onsager reciprocity, with linear scaling in both

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We theoretically investigate the transverse magnetization and ferroaxial moments induced by electric field gradients arising from the geometry of finite systems. Based on the Kubo formalism and real-time numerical simulations for a finite trapezoidal model, we demonstrate that both quantities are generated under the electric field gradient and are enhanced by tuning the leg inclination, which controls the gradient strength. We further show that the induced transverse magnetization is antisymmetric and linear in the magnetic field; such a response is prohibited by Onsager reciprocity in the absence of an electric field gradient. In addition, we find that the total transverse magnetization scales linearly with the electric field, in contrast to the longitudinal one, which exhibits a quadratic dependence, providing an advantage for experimental observation. Our results establish geometry-induced electric field gradients as a versatile mechanism for realizing and controlling unconventional transverse responses in mesoscopic systems.

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cond-mat.mes-hall 2026-05-12 2 theorems

The paper models the spin Seebeck effect in compensated ferrimagnet-normal metal…

Spin Seebeck effect in magnetic junctions with a compensated ferrimagnet

Exchange asymmetry produces magnon splitting that generates spin currents comparable to ferromagnets, while the effect vanishes in altermagn

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Compensated ferrimagnets enable ferromagnet-like spin transport without net magnetization. We study the spin Seebeck effect in a compensated ferrimagnet/normal-metal junction using a four-sublattice model in which sublattice inequivalence arises from differences in exchange couplings, in contrast to the previously studied anisotropy-based mechanism. Within the nonequilibrium Green's function framework, we show that isotropic magnon splitting generates a robust spin current with a magnitude comparable to that in standard ferromagnetic junctions. We also demonstrate that the spin Seebeck effect vanishes in altermagnet junctions under identical conditions, thereby establishing compensated ferrimagnets as uniquely suited for thermal spin-current generation among magnetically compensated systems. These results provide a theoretical basis for the applications of compensated ferrimagnets with exchange-coupling asymmetry as stray-field-free spin-current sources in spintronic devices.

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cond-mat.mes-hall 2026-05-11 Recognition

InSe on resonant SiN waveguide shortens exciton decay threefold

Purcell enhancement in layered InSe on the Mie-resonant silicon nitride waveguide

Mie resonance overlaps InSe emission band to couple excitons into guided modes and accelerate recombination.

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Hybrid integration of layered van der Waals (vdW) semiconductors with dielectric resonant structures provides an effective approach for controlling excitonic emission dynamics. Here, we demonstrate Purcell-enhanced spontaneous emission from a thin InSe flake integrated with a Mie-resonant Si$_3$N$_4$ waveguide. The structure is designed to spectrally overlap with the InSe photoluminescence band and enhance coupling of excitonic emission to the guided mode. Time-resolved photoluminescence shows a reduction of the excitonic decay time by up to a factor of three relative to planar InSe. The extracted Purcell factors are approximately 3 for out-of-plane excitons and 2.1 for in-plane excitons. These results demonstrate resonator-induced control of excitonic recombination in layered InSe and highlight vdW-dielectric interfaces as a platform for integrated excitonic and quantum photonic devices.

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cond-mat.mes-hall 2026-05-11 2 theorems

Interference reveals coherence in dark exciton condensate

Coherence, long-range transport and nuclear polarization in a driven-dissipative dark exciton condensate

Dark dipolar excitons in quantum wells show millimeter-scale transport and nuclear polarization locked by driven-dissipative gain-loss.

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We report direct evidence for macroscopic coherence in a condensate of dark dipolar excitons in coupled quantum wells and show that its formation follows a non-equilibrium, driven-dissipative mechanism. The condensation transition is governed by gain-loss competition, in which the exceptionally long lifetime of dark excitons enables their dominance in mode selection. Condensate formation is revealed by photoluminescence darkening, changes in radiative recombination channels, and the emergence of long-range hydrodynamic transport manifested by propagation of density (sound) modes over millimeter-scale distances. The buildup of dark exciton density induces dynamic nuclear polarization, which closes the dark-bright exciton gap, \Delta, via the Overhauser field. This leads to nuclear spin polarization across the entire mesa, far beyond the optically excited region, and produces pronounced hysteresis behavior. At \Delta ~ 0 the gap is locked and the condensate loss are minimal, resulting in a second threshold manifested as a photoluminescence blueshift. Coherence is revealed through interference between incident and boundary-reflected exciton currents, producing spatial modulation of the photoluminescence from the radiative reservoir and enabling extraction of the condensate coherence length. These results establish dark excitons as a platform for coherent quantum fluids in a driven-dissipative, strongly interacting regime with electrical tunability, bridging the physics of polariton condensates and matter-like excitonic systems.

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cond-mat.mes-hall 2026-05-11 2 theorems

Spin systems follow a topological Hooke's law

Spin Elasticity:A New Paradigm for Spintronics

Linking torque to morphology predicts oscillations, resonance, and spin stress waves in a unified tau-D framework.

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Elasticity shapes our world. For centuries, it has been regarded as a property exclusive to ordinary matter. Here we uncover its hidden existence in the spin degree of freedom. We introduce spin elasticity-a framework linking spin torque to spin morpgology. This reveals a topological Hooke's law, uncovers spontaneous oscillations and resonance, and predicts a new class of collective excitations:spin stress waves. By establishing a unfied tau-D theory bridging classical elasticity and topological spin physics, this work completes the elastic picture and opens a new frontier for spintronics-spinelastronics.

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cond-mat.mes-hall 2026-05-11 1 theorem

SAF asymmetry stabilizes antiparallel states with weaker coupling

Magnetization alignment in spin-transfer-torque magnetic random-access memory

Phase diagrams for 30 nm pillars reveal how layer differences reduce required coupling and alter reversal barriers in p-STT-MRAM.

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Reliable operation of perpendicular spin-transfer-torque magnetic random-access memory (p-STT-MRAM) requires control of magnetic alignment within the synthetic antiferromagnet (SAF) reference layer. At nanopillar dimensions, however, devices can exhibit magnetic states that are absent in extended thin films. We present a systematic micromagnetic study of 30 nm-diameter three-layer p-STT-MRAM nanopillars using experimentally motivated material parameters, and map equilibrium states as functions of bilinear and biquadratic interlayer exchange coupling. Phase diagrams show that introducing asymmetry between the SAF layers in saturation magnetization, anisotropy, and thickness reduces the coupling strength required to stabilize antiparallel SAF states and suppress competing configurations. Minimum-energy path calculations show that, for noncollinear antiparallel SAF states, increasing SAF asymmetry can raise SAF reversal barriers while lowering the free-layer barrier; this trade-off is absent for collinear antiparallel SAF states. Stray fields also significantly modify both SAF and free-layer energy barriers. To support the design of p-STT-MRAM devices with either collinear or noncollinear antiparallel SAF reference states, we publicly release the simulation dataset covering 4374 distinct device configurations.

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cond-mat.mes-hall 2026-05-11 Recognition

Coupling phase maps polarization to unify chirality types

Theory and Experiment of Chirality-induced Magnetic Nonreciprocity Manifested by Coupling Phase

Framework links field polarization to complex coupling phase and validates it experimentally for both conventional and synthetic magneticnon

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Magnetic interactions have long served as the most robust and widely used approach for realizing nonreciprocity, with an externally applied magnetic field breaking time-reversal symmetry (TRS) and chiral photon-magnon interactions introducing spatial asymmetry. In this work, we investigate the chirality mechanisms essential for magnetic nonreciprocity from a unified experimental and theoretical perspective. We begin by examining conventional chiral interactions that generate chiral electromagnetic fields through specially designed structures, and then place particular emphasis on synthetic chirality enabled by nontrivial phase accumulation in traveling-wave-mediated coupling systems. We establish a microscopic theoretical framework that maps field polarization onto the phase of a complex coupling strength and validate it with systematic experiments, thereby providing a consistent formalism that describes both conventional and synthetic chirality. Notably, we highlight the symmetry properties and the unique features of synthetic chirality that distinguish it from conventional nonreciprocal mechanisms.

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cond-mat.mes-hall 2026-05-11 2 theorems

Tunneling-to-scattering ratio sets PL polarization sign in magnetic TMD stacks

Effect of spin-dependent tunneling and intervalley scattering in magnetic-semiconductor van der Waals heterostructures on exciton and trion polarization

Model links spin-dependent charge transfer and intervalley lifetimes to switchable exciton emission under circular light

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We present a theoretical analysis of valley pseudospin control in the transition metal dichalcogenide (TMD) monolayer by utilizing the magnetic proximity effect of 2D magnetic layer and, propose self-consistent analysis of photoluminescence (PL) polarization peculiarities in TMD/magnetic material van der Waals heterostructures. We attribute observed peculiarities to the interplay between spin-dependent interlayer charge transfer and intervalley scattering of excitons and trions. The ratio between the electron tunneling timescale and the exciton and trion intervalley scattering lifetimes and radiative lifetimes determine the PL dynamics. A possibility to switch PL polarization sign due to the quasi-particles dynamics under circularly polarized laser excitations is revealed. We also discuss generalization of the proposed model due to the careful analysis of both intervalley and intravalley scattering processes between bright and dark excitons. Obtained results allow a long-distance manipulation of exciton and trion behaviors and open the possibilities for the effective control under spin and valley pseudospin in multilayer magnetic-semiconductor van der Waals heterostructures.

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cond-mat.mes-hall 2026-05-11 Recognition

Charged tips create and steer magnetic skyrmions

Manipulation of magnetic skyrmions by non-uniform electric fields

Non-uniform electric fields from a tip create, drive, and annihilate skyrmions in ferromagnetic films without currents.

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Magnetic skyrmions are topologically protected spin textures in ferromagnetic materials that hold great promise for both classical information storage and processing, as well as for fault-tolerant quantum computing. Realizing practical skyrmion-based devices demands an energy-efficient and precise method for their flexible manipulation. In this paper, we theoretically propose such a tool, leveraging the magnetoelectric effect induced by a localized electric field generated by one or several charged tips. Combining complementary numerical simulations and analytical approaches, we develop a consistent theory describing the stability and dynamics of N\'eel-type skyrmions under the influence of the electric field from a charged tip. Specifically, we demonstrate that the electric field can create, drive, and annihilate skyrmions of both chiralities, as well as more complex textures such as skyrmioniums and target skyrmions. We identify several distinct dynamical regimes of skyrmion motion near the tip and map them onto a phase diagram. Finally, we discuss the feasibility of a practical device capable of controlled skyrmion manipulation based on this principle.

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cond-mat.mes-hall 2026-05-11 2 theorems

Modular calculations predict adsorbate charge states on thin oxides

An ab initio approach to energy alignment and charge-state prediction of adsorbates on ultrathin insulators

GW energies, substrate polarization, pinning and dipole shifts are added to avoid full-stack simulations while exposing each contribution to

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The rapid progress of electron spin resonance scanning tunneling microscopy experiments has enabled the manipulation of individual adsorbate spin states physisorbed on ultrathin oxide layers supported on metal substrates. Electron resonance requires unpaired spin density on the adsorbate, which can be achieved, for instance, through charge transfer from the supporting substrate. This requires the correct energy-level alignment between the energy levels of the adsorbate and the Fermi energy of the substrate. Experiments on molecules and single atoms adsorbed on metal-insulator systems have revealed complex phenomena, including electronic bandgap narrowing, charge transfer, Fermi-level pinning, and the re-ordering of adsorbate orbitals after charge transfer. Despite these advances, a predictive first-principles approach based on accurate methods such as quasiparticle GW, capable of capturing these effects without the prohibitive cost of full adsorbate/oxide/metal simulations, remains an open challenge. In this work, we present a theoretical approach to determine the energy-level alignment of adsorbates on oxide/metal substrates. Our method transparently exposes all physical processes and strikes a balance between computational cost and accuracy. Ionization potentials and electron affinities of the isolated adsorbates are obtained using GW calculations, electronic bandgap polarization is quantified through the quasiparticle renormalization caused by the substrate, Fermi-level pinning is evaluated within the integer charge transfer model, and work function shifts arising from Pauli pushback or from the adsorbate-metal dipole are determined from the local variations of the electrostatic potential. This computationally efficient framework paves the way for highthroughput screening of molecular qubits and organic electronic interfaces.

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cond-mat.mes-hall 2026-05-11 2 theorems

Injection and shift currents unify via one quantum-geometric dipole

Emergent Quantum-Geometric Equivalence of Injection and Shift Currents

In linear-dispersion Dirac and Weyl semimetals at low energies, both currents are controlled by the same interband dipole.

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Injection and shift currents are generally regarded as distinct nonlinear optical responses with separate microscopic origins. Here, we uncover a general hidden connection between them through interband Berry-curvature and quantum-metric dipoles. In systems with approximately linear electronic dispersion near the Fermi level and at low photon energies, this relation sharpens into an emergent equivalence, with injection and shift currents governed by the same interband quantum-geometric dipole. This regime is naturally realized in Dirac and Weyl semimetals, as well as in strained graphene, where measurements of injection and shift currents probe a unified geometric property of the electronic wavefunctions rather than distinct dynamical processes. Our results establish a new framework for interpreting nonlinear optical experiments and suggest that quantum geometry may provide a broader organizing principle linking seemingly distinct nonlinear optical responses in solids.

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cond-mat.mes-hall 2026-05-11 2 theorems

Quantum geometry equates injection and shift currents

Emergent Quantum-Geometric Equivalence of Injection and Shift Currents

In Dirac and Weyl semimetals with linear bands, both currents arise from one interband dipole rather than separate processes.

abstract click to expand

Injection and shift currents are generally regarded as distinct nonlinear optical responses with separate microscopic origins. Here, we uncover a general hidden connection between them through interband Berry-curvature and quantum-metric dipoles. In systems with approximately linear electronic dispersion near the Fermi level and at low photon energies, this relation sharpens into an emergent equivalence, with injection and shift currents governed by the same interband quantum-geometric dipole. This regime is naturally realized in Dirac and Weyl semimetals, as well as in strained graphene, where measurements of injection and shift currents probe a unified geometric property of the electronic wavefunctions rather than distinct dynamical processes. Our results establish a new framework for interpreting nonlinear optical experiments and suggest that quantum geometry may provide a broader organizing principle linking seemingly distinct nonlinear optical responses in solids.

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cond-mat.mes-hall 2026-05-11 Recognition

Reduced Fokker-Planck model reaches ultra-low switching errors in Mn3Sn

Fokker--Planck framework for stochastic octupole moment dynamics in chiral antiferromagnet Mn3Sn

The single-moment description matches full three-sublattice simulations while accessing rare-event probabilities beyond direct Monte Carlo.

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We develop a reduced stochastic framework for thermally assisted octupole moment dynamics in Mn3Sn by combining the reduced Landau--Lifshitz--Gilbert (LLG) equation with the Fokker--Planck formalism. The reduced model is benchmarked against the complete three-sublattice octupole dynamics and is shown to capture the essential switching behavior with good accuracy. We then derive the corresponding Fokker--Planck equation, which is implemented and solved via a CUDA-accelerated solver. The analysis shows that the octupole dynamics are highly sensitive to the out-of-plane grid resolution because ultrafast rotation of the octupole is controlled by its very small deviations from the basal plane. The solver is validated against Monte Carlo simulations through equilibrium distributions, relaxation trajectories, and switching times. Finally, we apply the method to thermally assisted field-driven switching and demonstrate efficient access to ultra-low error probabilities beyond the practical reach of direct Monte Carlo simulations.

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cond-mat.mes-hall 2026-05-11 1 theorem

Staggered phonon chirality couples to Néel order

Antiferro-Chiral Phonons in mathcal{P}mathcal{T}-Symmetric Antiferromagnets

In PT-symmetric antiferromagnets, hybrid modes acquire both Raman and infrared character with zero net but finite staggered angular momentum

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Chiral phonons provide a route to couple lattice motion to magnetic order, but conventional chiral phonons carry a net angular momentum and thus couple naturally to net magnetization rather than to compensated N\'eel order. Here we show that $\mathcal{P}\mathcal{T}$-symmetric antiferromagnets can host \emph{antiferro-chiral phonons} (AFCPs): phonon modes with vanishing total angular momentum but finite sublattice-staggered angular momentum. Symmetry enforces this distinction because $\mathcal{P}\mathcal{T}$ forbids a net phonon angular momentum while allowing counter-rotating local motion on inversion-related sublattices. AFCPs arise from a N\'eel-vector-locked coupling between Raman and infrared-active phonons. The coupling is odd under both $\mathcal{P}$ and $\mathcal{T}$ while preserving their product. Through this hybridization, the normal modes acquire both Raman and infrared character and carry a sublattice-staggered phonon angular momentum that acts as a conjugate field to the N\'eel vector. This coupling is microscopically generated by the molecular Berry curvature, which is demonstrated in a prototype lattice model. Reversing the N\'eel vector reverses the staggered phonon chirality. These results indicate AFCPs as probes of antiferromagnetic order and suggest coherent phonon excitation as a route to its dynamical control.

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cond-mat.mes-hall 2026-05-11 2 theorems

PT-symmetric antiferromagnets support phonons with staggered angular momentum

Antiferro-Chiral Phonons in mathcal{P}mathcal{T}-Symmetric Antiferromagnets

The modes carry zero net angular momentum yet couple directly to compensated Néel order and reverse when the magnetic vector flips.

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Chiral phonons provide a route to couple lattice motion to magnetic order, but conventional chiral phonons carry a net angular momentum and thus couple naturally to net magnetization rather than to compensated N\'eel order. Here we show that $\mathcal{P}\mathcal{T}$-symmetric antiferromagnets can host \emph{antiferro-chiral phonons} (AFCPs): phonon modes with vanishing total angular momentum but finite sublattice-staggered angular momentum. Symmetry enforces this distinction because $\mathcal{P}\mathcal{T}$ forbids a net phonon angular momentum while allowing counter-rotating local motion on inversion-related sublattices. AFCPs arise from a N\'eel-vector-locked coupling between Raman and infrared-active phonons. The coupling is odd under both $\mathcal{P}$ and $\mathcal{T}$ while preserving their product. Through this hybridization, the normal modes acquire both Raman and infrared character and carry a sublattice-staggered phonon angular momentum that acts as a conjugate field to the N\'eel vector. This coupling is microscopically generated by the molecular Berry curvature, which is demonstrated in a prototype lattice model. Reversing the N\'eel vector reverses the staggered phonon chirality. These results indicate AFCPs as probes of antiferromagnetic order and suggest coherent phonon excitation as a route to its dynamical control.

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cond-mat.mes-hall 2026-05-11 2 theorems

Bosonic lattices measure energy-resolved Středa responses

Energy-Resolved Quantum Geometry from Stv{r}eda Response: Driven-Dissipative Bosonic Lattices and Disordered Systems

Uniform pumping and loss produce a Lorentzian filter that reconstructs quantum-geometry markers for topological bands under disorder.

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The St\v{r}eda formula links the Hall conductivity of an insulator to the magnetic-field response of its particle density, providing a local and universal probe of the topological Chern number. Beyond this quantized response, an energy-resolved St\v{r}eda marker can be defined from the magnetic response of the density of states, revealing detailed features of the quantum geometry of Bloch bands. We show that driven-dissipative bosonic lattices provide direct access to both the integrated and energy-resolved St\v{r}eda responses. Our scheme uses controlled pumping with uniform strength and random phases across the lattice, together with uniform loss, to yield a Lorentzian filter of eigenmode occupations. For generic dispersive bands, this enables reconstruction of a coarse-grained energy-resolved St\v{r}eda response, establishing these platforms as versatile probes of anomalous spectral flow and energy-resolved quantum geometry. As a striking application, we show that this marker elucidates the fate of topological bands under strong disorder, capturing the quantum-geometric structure underlying topological Anderson insulators.

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cond-mat.mes-hall 2026-05-11 2 theorems

Chirality flips photocurrent signs inside finite-q window

Finite-q photon-drag shift current in two-dimensional massive chiral Dirac fermions

For J=1 the current stays positive; for J≥2 zero contours and reversals appear within the allowed momentum region.

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We investigate the photon-drag shift current in an isotropic single-valley two-dimensional massive chiral Dirac model with chirality index $J=1,2,3$ by directly evaluating the full finite-$q$ non-vertical response beyond the perturbative small-$q$ regime. Our central result is that chirality qualitatively reorganizes the sign topology of the finite-$q$ photocurrent $\mathbf{ j}(\mathbf{ q})$. For $J=1$, the photocurrent remains broadly positive, whereas higher-chirality sectors ($J \ge 2$) generically develop internal zero-current contours and sign reversals within the kinematically allowed region. We further show that the photocurrent is symmetry-constrained to be purely transverse, $\mathbf{j}(\mathbf{q}) \propto \hat{\mathbf{z}}\times\mathbf{q}$, and vanishes in the strictly vertical-transition limit $q=0$ in centrosymmetric systems. Pauli blocking further shapes the response by selecting the active portion of the resonance contour, while its extinction at large $\Delta$ or $q$ follows from a simple kinematic cutoff. These results establish the isotropic massive chiral Dirac problem as a symmetry-controlled benchmark for chirality-dependent finite-$q$ shift currents.

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cond-mat.mes-hall 2026-05-11 2 theorems

Bias system stabilizes sub-20 nm skyrmions at zero field

Bias-Engineered Synthetic Antiferromagnets Hosting sub-20 nm Zero-Field Skyrmions at Room Temperature

A compensated SAF layer suppresses domains and supplies uniform exchange, enabling the smallest reported zero-field skyrmions at room temp.

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Synthetic antiferromagnetic skyrmions (SAFsk) are nanoscale, topologically protected spin textures with strong potential for spintronic technologies because of their high stability and the absence of the skyrmion Hall effect. However, robust zero field stabilization remains a central challenge. Here, a synthetic antiferromagnetic (SAF) bias system is introduced as a novel strategy to stabilize both ferromagnetic skyrmions (FMsk) and SAFsk at zero field. Ferromagnetic (FM) and SAF multilayers are designed, fabricated and integrated with the SAF bias system to enable controlled skyrmion stabilization and polarity setting via multilayer design and a preparatory field cycle. Combining quantitative and high-sensitivity magnetic force microscopy (MFM) with micromagnetic modeling, reliable zero field skyrmion formation is demonstrated and sub 20nm SAFsk are directly observed, the smallest SAFsk reported to date. Moreover, the SAF bias system concept introduced here offers a robust and scalable route to bias future skyrmion multilayers, as its compensated nature suppresses domain formation and preserves a uniform exchange field.

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cond-mat.mes-hall 2026-05-11 Recognition

Excitons let light control friction in nanochannels

Exciton-mediated optical control of liquid-solid friction

Theory shows coupling to water charges reduces slip and diffusion in nanotubes without fitting parameters.

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Interfacial friction in nanofluidic systems can arise from fluctuation-induced coupling between liquid charge fluctuations and the internal excitations of the confining solid. Here, we develop a microscopic theory of exciton-mediated solid-liquid friction based on the coupling between optically generated excitons and charge fluctuations in water. We distinguish between static excitons, localized by disorder or functionalization, and dynamic excitons, which interact with water through polarization fluctuations. In both cases, we derive analytical formulas for the excitonic friction, which is experimentally tunable and can significantly reduce the slip length and thereby the hydraulic permeability of nanochannels. Applying our framework to carbon nanotubes, we quantitatively reproduce the recent measurements of Kistwal et al., showing a reduction of nanotube diffusion under optical excitation, without fitting parameters. More broadly, our results establish excitons as a mechanism to optically control nanofluidic transport and suggest that excitonic photoluminescence could provide an optical probe of flow velocity inside nanochannels.

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cond-mat.mes-hall 2026-05-11 2 theorems

Damped magnons show skin effect in skyrmion strings

Point-gap topology of damped magnon excitations in skyrmion strings

Point-gap winding numbers appear from local damping alone and equal the sign of k at band minima under unidirectional nonlocal damping, dict

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We theoretically study the non-Hermitian topology of magnons with finite lifetimes due to Gilbert damping. By incorporating the spin-wave theory and perturbation theory for the Landau-Lifshitz-Gilbert equation including nonlocal damping terms, we analytically evaluate the spectral winding number for point gaps, which indicates the existence of the non-Hermitian skin effect (NHSE). We find that the NHSE can occur even in the absence of nonlocal damping. In the presence of nonlocal damping along one direction, we show that the winding number for an energy band with a unique minimum is determined from the sign of the wave number at the band minimum. We demonstrate these results using a model that hosts a skyrmion-string lattice as a steady state. We further investigate spin-wave propagation dynamics excited by a magnetic-field pulse and show that the propagation direction changes drastically from band to band depending on the presence of local and nonlocal damping, consistent with the nontrivial winding numbers.

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cond-mat.mes-hall 2026-05-11 2 theorems

Effective damping in 1D spin chains varies with temperature and momentum

Effective Gilbert damping in the stochastic Landau-Lifshitz-Gilbert equation

Fits to the dynamical structure factor from stochastic trajectories show deviations from constant Gilbert damping due to bath interactions.

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Quasi particle based (e.g. Boltzmann equation) studies of spin wave transport often assume that their scattering rates follow the simple form $\eta=\alpha \omega$, with the Gilbert damping $\alpha$ and frequency $\omega$. In this work, we examine the effective damping $\alpha_{eff,T}=\eta/\omega$ observed in atomistic spin dynamics, when temperature and spin wave interactions are introduced for a 1D spin chain. We extract the dynamical correlation functions from spin trajectories propagated using the stochastic Landau-Lifshitz-Gilbert equation, and fit the dynamical structure factor, yielding the dispersion and scattering rates for a wide range of temperatures. The resulting effective damping can be very different from the initially constant Gilbert value. It exhibits a temperature and crystal momentum scaling which we explain based on interactions with the Gilbert bath and spin wave scattering by changes in local magnetic order.

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cond-mat.mes-hall 2026-05-11 Recognition

Point-gap topology around spectrum origin enforces non-Markovian feedback

Topological Characterization of Discrete-Time Classical Stochastic Processes: Dual Role of Point-Gap Topology

Nontrivial winding around zero in stochastic matrices requires feedback-induced memory, simulable by Markovian quantum master equations.

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We present topological characterization of classical stochastic processes described by discrete-time Markov chains on lattices. We point out that point-gap topology of stochastic matrices entails two distinct physical consequences that hinge on the choice of the reference point. The point-gap topology around a generic reference point is related to the direction of transport, and nontrivial topology around the origin of the complex spectrum of a stochastic matrix implies non-Markovianity caused by, e.g., feedback control. On the basis of this characterization, we identify the topological origin of directed transport in a classic experiment of Maxwell's demon [S. Toyabe et al., Nat. Phys. 6, 988 (2010)] and find the topological nature of feedback control beyond thermodynamic interpretation. We demonstrate that a topologically enforced non-Markovian classical stochastic process can be simulated by a Markovian quantum master equation, indicating a topological form of quantum advantage.

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cond-mat.mes-hall 2026-05-11 1 theorem

Termination geometry alone selects edge or corner states in antiferromagnets

Hybrid-order topology in two-dimensional nonsymmorphic antiferromagnets

In one bulk insulating phase of 2D nonsymmorphic antiferromagnets, boundary shape decides between gapless edges and zero-energy corners.

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We theoretically demonstrate hybrid-order topology in a two-dimensional nonsymmorphic antiferromagnet. Utilizing a generic antiferromagnetic Dirac model with a symmetry-allowed, momentum-dependent spin-density-wave (SDW) mass, we show that a single bulk insulating phase exhibits distinct topological boundary manifestations governed solely by the termination geometry. For screw-compatible edges, nonsymmorphic screw symmetry protects gapless first-order edge states. In contrast, for a $45^\circ$ diamond-shaped termination, the screw symmetry is broken at the boundary, resulting in gapped edges. However, the finite geometry still preserves magnetic mirror symmetries $\mathcal{M}_x\mathcal{T}$ and $\mathcal{M}_y\mathcal{T}$, which enforce an alternating pattern of edge masses, thereby binding zero-dimensional corner states. This second-order phase is characterized by a quantized quadrupole moment, with corner states pinned to zero energy by the chiral symmetry. We further demonstrate that explicit lattice perturbations can selectively gap the first-order edge modes while robustly preserving the corner states. Our work establishes a symmetry-based route to a termination-controlled duality between first- and second-order topology in magnetic nonsymmorphic systems.

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cond-mat.mes-hall 2026-05-11 2 theorems

Strain and oblique light create Floquet corner modes in graphene

Floquet second-order topological insulator in strained graphene

Uniaxial strain plus elliptically projected circular drive gaps edges while protecting zero-dimensional states at corners of finite flakes.

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Graphene provides a canonical setting for Floquet band engineering, where circularly polarized light can dynamically open topological gaps at Dirac points and generate nonequilibrium Hall responses. Here we show that uniaxial strain and off-resonant circularly polarized light with tunable incidence angle enable a controllable route to Floquet higher-order topology in graphene. Using a strained honeycomb tight-binding model with Peierls coupling and a high-frequency expansion for the effective Floquet Hamiltonian, we find that strain drives the Dirac cones toward the Dirac-merging (semi-Dirac) critical regime, where the light-induced mass becomes strongly anisotropic. For oblique incidence, the projected drive is effectively elliptically polarized and, in combination with strain, stabilizes a phase with gapped edges but robust in-gap corner modes in finite geometries, realizing a Floquet second-order topological insulator. We characterize the phase diagram via the Chern number and a crystalline-symmetry-quantized polarization invariant. Finally, first-principles-informed tight-binding calculations corroborate the predicted topological evolution in strained graphene nanostructures. Our results identify driven strained graphene as a realistic and tunable platform for realizing and diagnosing Floquet higher-order topological phases.

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cond-mat.mes-hall 2026-05-11 2 theorems

Asymmetric barrier creates nonreciprocal flow in Dirac semimetals

Coherent Nonreciprocal Valley Transport in Dirac/Weyl Semimetals

Geometry alone produces directional transport asymmetry without magnetic fields or built-in material order.

abstract click to expand

Nonreciprocal electronic transport, defined as a directional asymmetry between the forward and backward two-terminal responses, typically requires a built-in inversion-breaking feature of the host material or an applied field, such as magnetic order, magnetochiral coupling, polar lattice distortion, or a superconducting state. Here, we show that a single electrostatic barrier whose shape lacks inversion symmetry can drive coherent nonreciprocal transport in a Dirac or Weyl channel without any of these ingredients. The mechanism is geometric: across a barrier with two qualitatively distinct refraction interfaces (one vertical and one oblique), forward- and backward-propagating wave packets experience different Fermi-surface-mismatch sequences at the entrance and exit faces. Using coherent split-operator Dirac wave-packet simulations with realistic device parameters, we show that in a channel with isotropic (untilted) energy dispersion, an inversion-asymmetric (right-angle) triangular barrier produces strong charge-mode rectification, establishing its purely geometric origin. Adding a Dirac-cone tilt turns the same shape into a coherent valley-resolved diode whose dichroic structure flips sign across the Dirac point. Strikingly, a mirror-symmetric (isosceles) triangle with two oblique faces exhibits valley-polarized transmission while remaining exactly reciprocal. Oblique interfaces and tilt together do not suffice; the essential ingredient is a sequence of geometrically distinct interface types.

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cond-mat.mes-hall 2026-05-08 2 theorems

Fermi-surface electrons enhance phonon magnetic moments in metals

Nonadiabatic Theory of Phonon Magnetic Moments in Insulators and Metals

A nonadiabatic theory including finite-frequency effects brings predictions for PbSnTe up to the observed experimental scale.

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We develop a nonadiabatic theory of phonon magnetic moments applicable to both insulators and metals. By relating the phonon magnetic moment to the force-velocity response of ions in a magnetic field, we derive a gauge-invariant expression using a gauge-covariant Wigner expansion. The formalism naturally separates Fermi-sea and Fermi-surface contributions and captures the full dependence on phonon frequency. In gapped systems, our theory reduces to previous adiabatic expressions in the low-frequency limit. Beyond this limit, it reveals additional contributions arising from resonant interband processes and the Fermi surface. Applying our theory to Pb$_{1-x}$Sn$_x$Te, we find that the Fermi-surface contribution substantially enhances the phonon magnetic moment, reproducing the same order of magnitude as the experimental observation. Our results provide a unified framework for describing phonon magnetic moments beyond the adiabatic regime.

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cond-mat.mes-hall 2026-05-08 2 theorems

This paper develops an analytical framework using the Bogoliubov-de Gennes approach to…

Majorana bound states in chiral ferromagnet-superconductor heterostructures revisited

Analytical expressions for Majorana bound states in skyrmion-vortex pairs demonstrate that spin-orbit coupling is essential for their…

abstract click to expand

Majorana zero modes are central to the pursuit of fault-tolerant topological quantum computation. While traditionally sought in one-dimensional hybrid nanowires, a robust alternative platform involves heterostructures combining superconductors with noncollinear magnets. This work focuses on a particularly promising system: a chiral ferromagnet hosting a magnetic skyrmion coupled to a superconducting film containing a superconducting vortex. Such skyrmion-vortex pairs have recently been realized experimentally and are theorized to harbor localized Majorana states, offering a potential pathway for braiding operations. We present a comprehensive theoretical analysis of the low-energy quasiparticle bound states in these heterostructures. Extending previous studies, we develop an analytical framework for the Majorana wavefunctions as well as the wavefunctions and spectrum of other lowlying states within a Bogoliubov-de Gennes approach. Our analytical results explicitly demonstrate the critical role of spin-orbit coupling for the stabilization of Majorana modes and provides approximate analytical expressions for low-lying states localized at the vortex, both with and without an accompanying skyrmion. The derived analytical results show excellent agreement with numerical simulations. We further elucidate the role of realistic effects, including vector potentials and texture perturbations from stray magnetic fields, to assess their impact.

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cond-mat.mes-hall 2026-05-08

Spin alignment cuts phonon scattering to cause colossal magnetoresistance

Colossal Magnetoresistance and Phonon Driven Exchange Dynamics in Eu₅Sn₂As₆

In Eu5Sn2As6, magnetic fields lift spin degeneracy and reduce scattering, allowing electrons to move more freely.

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The emergence of colossal magnetoresistance in a new generation of Eu$^{2+}$-based antiferromagnets is intriguing given stark contrasts to the archetypal perovskite manganites and doped Eu-chalcogenides. In this study the thermal conductivity and magnetostriction of Eu$_5$Sn$_2$As$_6$ -- one such representative -- have been measured to better understand the role of the crystal lattice. Both properties are strongly field-dependent and mirror the magnetization, saturating once the Eu$^{2+}$ moments are polarized. The field-enhancement of the phonon-dominated thermal conductivity is interpreted through the lifting of a degeneracy of spin configurations, and the subsequent saturation due to quenched magnetostrain in high field. Comparison with spin-glass insulators suggests that this phenomenon is not a byproduct but rather the driver of electron delocalization due to the suppression of strong phonon scattering arising from exchange frustration.

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cond-mat.mes-hall 2026-05-08

Current pulses heat 2D magnet above Curie point for low-field writing

Electrically controlled Heat Assisted Magnetic Recording in Intercalated 2D Magnets

In Ni1/4TaSe2, Joule heating lets a 2mT field write data while the anomalous Hall effect reads it out electronically.

abstract click to expand

The ever-increasing demand for fast, reliable, and energy-efficient information storage continues to push magnetic memory technologies toward their fundamental limits. Conventional scaling strategies, which rely on reducing bit size, inevitably run into the "magnetic recording trilemma," where signal-to-noise ratio, thermal stability, and writability cannot all be optimized simultaneously. Heat-assisted magnetic recording (HAMR) has emerged as the leading solution, enabling high-density storage by transiently heating the medium during the write cycle. However, the reliance on laser optics and plasmonic transducers restricts HAMR primarily to hard-disk drives, limiting its integration with on-chip or embedded architectures. Here, we demonstrate an electronic variant of HAMR in which Joule heating from low-current density current pulses facilitates data writing, while the anomalous Hall effect provides electronic readout. Employing intercalated 2D magnet Ni$_{1/4}$TaSe$_2$, we show direct evidence that current pulses heat the material above its Curie temperature, during which a small magnetic field of ~2mT (100 times smaller than the coercive field) enables efficient data writing. The all-electronic approach combined with the 2D magnetic medium creates timely opportunities to revisit the energy-assisted magnetization recording, enabling new recording schemes that combine fundamental novelty with technological impact.

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cond-mat.mes-hall 2026-05-08

Twisted kagome bilayers show higher-order magic angles

Twisted Kagome Bilayers: Higher-Order Magic Angles, Topological Flat Bands, and Sublattice Interference

Local band flattening arises from high-order Van Hove singularities, and twist alone produces non-trivial topology.

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We develop a low-energy continuum model to describe the moir\'{e} physics of heterostructures, which is a generalization of the celebrated Bistritzer-MacDonald (BM) method [R. Bistritzer and A. H. MacDonald, Proc. Natl. Acad. Sci. U.S.A. 108, 12233 (2011)]. We take as an example the moir\'{e} physics of electrons in twisted bilayer kagom\'{e} (TBK) metals near $1/3$ filling where monolayer Dirac cones lie. We demonstrate the emergence of higher-order magic angles where significant local band flattening occurs as a high-order Van Hove singularity emerges and show how twisting alone can induce non-trivial topology. We, furthermore, show that while sublattice interference effects are present, their role is not as prominent as in monolayer kagome.

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cond-mat.mes-hall 2026-05-08

Altermagnetic magnon bath adds nonlocal damping to LLG equation

Engineering a driven-dissipative bath of altermagnetic quantum magnons for controlling classical dynamics of spins hosting spin waves, domain walls, or skyrmions

Driven quantum magnons in attached layer enable tunable control of spin waves, domain walls and skyrmions through two anisotropic terms.

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Using Schwinger-Keldysh field theory (SKFT), we engineer a dissipative and driven (i.e., out of equilibrium) bosonic bath acting on classical localized spins within a ferromagnetic insulator (FI) layer whose dynamics is governed by the Landau-Lifshitz-Gilbert equation, as is usually assumed in spintronics and magnonics. The bosonic bath is comprised of quantum magnons within a layer of altermagnetic insulator (AMI) that is attached to a conventional FI layer, often one of the key ingredients within spintronic and magnonic multilayers, so that interaction between slow classical (in the FI layer) and fast quantum (in the AMI layer) localized spins ensues. Such a bath, including its driving to produce a nonequilibrium distribution of altermagnetic magnons, generates a rich structure of the SKFT-derived extended LLG equation for classical spins within the FI layer. Our LLG equation contains two damping terms, both of which are spatially nonlocal and anisotropic, while one of them is also intrinsically non-Markovian, i.e., nonlocal in time. We demonstrate how to exploit these terms for tuning spintronic and magnonic effects within the FI layer of AMI/FI bilayers that involve spin wave or domain wall propagation, as well as skyrmion annihilation.

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cond-mat.mes-hall 2026-05-08

Exchange coupling enables remote spin initialization in molecules

Electrical Spin Pumping in Exchange-coupled Molecules

A spin-polarized current sets the electron spin state of a neighboring molecule through angular momentum transfer.

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Electron spins in single molecules are a promising platform for quantum information processing. However, their practical implementation as qubits requires reliable control at the single-entity level, including an efficient state initialization. Here, we demonstrate the remote, all-electrical initialization of the electron spin in single molecules: Using electron spin resonance scanning tunneling microscopy, we investigate coupled pairs of S=1/2 molecules (Fe-FePc), where one molecule serves as a readout and pumping unit for the neighboring one. We show that the exchange interaction between them enables angular momentum transfer, which allows for the control of the remote spin state via the direction and magnitude of the spin-polarized tunneling current and the exchange coupling strength. These results establish a general, all-electrical approach for remote spin initialization that is readily transferable to a wide range of spin-based quantum architectures.

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cond-mat.mes-hall 2026-05-08

Genus of system shape protects higher-order topological states

Genus-protected higher-order topological phases

Corner and hinge modes survive surface changes in materials with holes when only bulk gap and local symmetries are maintained.

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Higher-order topological phases (HOTPs) feature protected gapless modes on boundaries of higher codimension, such as the corners or hinges of a crystal. They are understood as being protected by lattice symmetries: If the latter are broken, it becomes possible to remove the boundary modes without closing the bulk gap. In this work, we present construction schemes for HOTPs protected solely by the bulk gap, by fundamental symmetries, and by the global topology of the system shape (its genus, or number of holes), independent of any crystalline symmetries. As long as the fundamental local symmetries are preserved, the resulting boundary states cannot be removed by any purely-surface perturbation.

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cond-mat.mes-hall 2026-05-08

Anomalous Thomson coefficient triples Nernst at low temperatures

Anomalous Thomson Effect

Model-independent link converts existing Nernst data into large predicted Thomson values for refrigeration in CeCrGe3 near 77 K.

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We propose an effect named the anomalous Thomson effect (ATE), analogous to the anomalous Hall effect and the anomalous Nernst effect (ANE). The anomalous Thomson coefficient (ATC) is derived as a function of the anomalous Nernst coefficient (ANC); hence, the ATC inherits the same mechanisms of the ANC. Specifically, we study a massive Dirac model for Fe3Sn2 to capture intrinsic Berry-curvature-driven transport. Our results show that the ATC is generally enhanced relative to the ANC. In the low-temperature limit, the ratio ATC/ANC approaches three. Since the relation between the ATE and the ANE is model-independent, we utilize experimental ANE data to infer experiment-related ATC for CoS2, Co3Sn2S2, and CeCrGe3. We find that the ATC for CeCrGe3 can be as large as fifteen times the ANC in the liquid-nitrogen temperature regime, making this effect highly attractive for solid-state thermoelectric refrigeration in this temperature range. It is important to emphasize that the proposed ATE can be directly verified using existing ANE data, without the need for additional equipment or measurements.

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cond-mat.mes-hall 2026-05-08

High-resistivity silicon tops sub-kelvin heat conduction

Sub-kelvin thermal conductivity of substrates and on-chip routing in quantum integrated systems

The substrate remains the dominant heat path in systems with niobium routing lines.

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The development of large-scale quantum systems increasingly relies on the close integration of heterogeneous components such as qubits, control electronics, and readout circuits, making thermal management at cryogenic temperatures a central challenge in such architectures. In this work, we present an experimental thermal study of two building blocks of such systems: the substrate and the on-chip routing. We first investigate the sub-kelvin thermal conductivity of four substrate materials: high-resistivity silicon, low-resistivity silicon, borosilicate, and sapphire. We report that high-resistivity silicon exhibits the highest thermal conductivity among the substrates studied ($5\cdot10^{-2}$~W/m$\cdot$K at 300~mK), while low-resistivity silicon, borosilicate, and sapphire show lower values ($8\cdot10^{-4}$~W/m$\cdot$K, 2$\cdot10^{-3}$~W/m$\cdot$K, and 2$\cdot10^{-3}$~W/m$\cdot$K at 300~mK, respectively). Ballistic conductance evaluation using a finite-element non-equilibrium Green's function approach further allows us to extract the phonon mean free path in each substrate and gives insights into the involved scattering mechanisms. Additionally, we employ a dedicated test vehicle to evaluate the impact of on-chip routing on the thermal conductance of the system. Our measurements with superconducting Nb routing lines reveal that the routing increases the in-plane thermal conductance of the system, but the substrate remains the dominant heat path. These results highlight the critical role of the substrate choice within quantum systems and underscore the importance of function partitioning through 3D integration approaches for more efficient thermal management in quantum architectures.

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cond-mat.mes-hall 2026-05-08

Nodal-line semimetals yield two quantum oscillation frequencies

Quantum oscillations and nonsaturating magnetoresistivity in nodal-line semimetals

The torus Fermi surface creates dual frequencies as an experimental signature, though magnetoresistivity is nonsaturating with modest ratio.

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Understanding the magnetotransport behaviors in topological systems remains alluring, as a lot of intrinsic information could be extracted, e.g., the band structures, Berry phase, Fermi surface, carrier density, and so on. Motivated by the recent magnetotransport developments in nodal-line semimetal, EuGa4, in this paper, we will study the magnetotransport properties of the system, focusing on the quantum oscillations and nonsaturating magnetoresistivity (MR). Firstly, we analyze the chemical potential and magnetoconductivity oscillations with the magnetic field and reveal that there exist two distinct oscillation frequencies, which are caused by the characteristic torus Fermi surface and can be regarded as an important experimental signature of nodal-line semimetals. Then we calculate the MR and find that although the MR is nonsaturating with the magnetic field in the low-energy region, the MR ratio is much smaller than that reported in the experiment.

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cond-mat.mes-hall 2026-05-08

Giant DM interaction flags coherent CISS in chiral molecules

Dzyaloshinskii-Moriya interaction as a coherence diagnostic for chirality-induced spin selectivity

Unitary spin rotation produces |D|/J_H up to 3 while incoherent filtering forces D exactly to zero, enabling a direct qubit test.

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Whether chirality-induced spin selectivity (CISS) reflects coherent SU(2) spin rotation or incoherent spin-dependent filtering is a central unresolved question in molecular spintronics, with implications ranging from asymmetric chemistry to quantum information. We show that these two scenarios are distinguishable by a sharp symmetry criterion on the superexchange interaction mediated by a chiral molecular bridge. Coherent CISS, implemented as a unitary spin rotation of the tunneling electron, generates a giant Dzyaloshinskii-Moriya (DM) interaction with ratio |D|/JH up to 3, which is two orders of magnitude beyond intrinsic Rashba spin-orbit coupling in Si/SiGe. Incoherent CISS, represented by any Hermitian (non-unitary but spin-diagonal) tunneling matrix, produces D = 0 identically; we prove this as a structural theorem, reinforced by a Lindblad argument that dissipative spin filtering cannot modify virtual-tunneling-mediated superexchange. The DM interaction thus serves as a coherence order parameter, nonzero only when quantum amplitudes for opposite-spin transmission maintain a fixed relative phase. We derive closed-form angular, enantiomeric, and sensitivity signatures and show that the critical coherent rotation angle lies two orders of magnitude below current transport-inferred values and is accessible to existing 10 kHz exchange spectroscopy in gate-defined quantum dots. Five candidate molecules are predicted to exceed this threshold by one to two orders of magnitude even in a conservative interface-amplification scenario. The proposed measurement converts a long-standing transport controversy into a binary spin-qubit experiment with quantum-amplitude resolution.

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cond-mat.mes-hall 2026-05-08

Sliding CDW converts DC current into Floquet sideband ladder

Intrinsic Floquet Generation and 1/I Quantum Oscillations in a Sliding Charge-Density Wave

Fixed-bias tunneling cuts the intrinsic ac states to yield 1/I oscillations, but only when current is confined to a narrow coherent filament

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The realization of intrinsic, tunable high-frequency quantum states without external radiation is a major goal in condensed matter physics and quantum device engineering. Here, we demonstrate that a uniformly sliding charge-density wave (CDW) acts as an intrinsic dc-to-ac converter, transforming spatial periodicity into temporal periodicity to realize a unique periodically driven quantum state. We show that the isolated sliding-CDW problem is exactly solvable in Floquet form, yielding split gap edges and a ladder of Floquet sidebands. Using this exact solution, we reveal that weak-probe tunneling spectroscopy naturally yields an inverse-current ($1/I$) oscillation as a fixed-bias cut of the sideband ladder. Matching the observed oscillation period to theory indicates that the macroscopic current must percolate through a highly localized coherent filament, with an effective channel number orders of magnitude smaller than the geometric chain count. Furthermore, using a segmented multiterminal model, we demonstrate that inelastic phase-slip dephasing near the contacts explains the strong suppression of oscillation visibility on outer voltage probes. Ultimately, our results provide a rigorous transport interpretation of the striking $1/I$ quantum oscillations recently observed in quasi-one-dimensional CDW insulators. More broadly, they highlight a universal spatial-to-temporal conversion mechanism where the insulating gap protects Floquet coherence, offering a novel paradigm for intrinsically driven quantum devices.

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cond-mat.mes-hall 2026-05-08

Even-integer spin conductance quantized in 2DEG-S hybrids

Emergent spin quantum Hall edge states at the boundary of two-dimensional electron gas proximitized by an s-wave superconductor

Topologically protected spin currents survive disorder at the edges while charge transport does not, enabling electrical detection of classC

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Hybrid two-dimensional electron gas-superconductor (2DEG-S) structures in a quantized magnetic field offer a promising platform for realizing new topological phases. While recent experiments reveal chiral Andreev edge states, their charge conductance is not integer quantized and is disorder sensitive, raising the question of whether topological protection survives. We argue that it does, but manifests in the spin transport channel. The 2DEG-S system belongs to symmetry class C of the Altland-Zirnbauer classification, which supports an even-integer quantized transverse spin conductivity - the spin quantum Hall effect, so far unobserved experimentally. We demonstrate that 2DEG-S hybrids host topologically protected edge states carrying a spin current with an even-integer quantized spin conductance robust against disorder. Finally, we propose an experimental setup to probe this protection via electrical measurements, establishing a concrete route to detect the class C origin of the chiral Andreev edge states.

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cond-mat.mes-hall 2026-05-08 Recognition

Spin quantum Hall states appear at 2DEG-superconductor boundary

Emergent spin quantum Hall edge states at the boundary of two-dimensional electron gas proximitized by an s-wave superconductor

Even-integer quantized spin current carried by protected edge states offers electrical test of class C topology.

abstract click to expand

Hybrid two-dimensional electron gas-superconductor (2DEG-S) structures in a quantized magnetic field offer a promising platform for realizing new topological phases. While recent experiments reveal chiral Andreev edge states, their charge conductance is not integer quantized and is disorder sensitive, raising the question of whether topological protection survives. We argue that it does, but manifests in the spin transport channel. The 2DEG-S system belongs to symmetry class C of the Altland-Zirnbauer classification, which supports an even-integer quantized transverse spin conductivity - the spin quantum Hall effect, so far unobserved experimentally. We demonstrate that 2DEG-S hybrids host topologically protected edge states carrying a spin current with an even-integer quantized spin conductance robust against disorder. Finally, we propose an experimental setup to probe this protection via electrical measurements, establishing a concrete route to detect the class C origin of the chiral Andreev edge states.

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cond-mat.mes-hall 2026-05-08

Majorana island dynamics leave lead transport statistics incomplete

Thermodynamic incompleteness in non-Markovian Majorana transport I: Island dynamics and missing transport statistics

Identical island tomography and relaxation can still produce different charge noise, heat noise, and charge-energy correlations in the leads

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We show that the complete knowledge of the non-Markovian island-state dynamics of a floating Majorana island does not, in general, determine the thermodynamic transport statistics measured in the leads. We demonstrate this statement in a Coulomb-blockaded island with $M$ Majorana zero modes coupled to structured reservoirs. In the cotunneling regime, a Schrieffer-Wolff transformation gives reservoir-assisted transitions generated by Majorana bilinears. After the reservoirs are traced out, the island state determines the memory kernel associated with each bilinear, and this is enough to predict all island-state observables within the cotunneling approximation. It is not enough to determine which lead or detector channel supplied the electron, absorbed the electron, or carried the corresponding energy exchange. This is a genuine loss of thermodynamic information, not an error in the island equation. We formulate the result as a thermodynamic completeness criterion: an island memory equation determines a transport observable only when that observable is constant over all assignments of reservoir channels that give the same island memory kernel. The criterion gives a measurable prediction. Two structured-reservoir Majorana devices can have identical island-state tomography and relaxation, but different charge noise measured separately in the leads, heat noise, and mixed charge-energy correlations. The geometry of the projection from reservoir records to island kernels and the topology of the network of tunnel contacts identify which transport information is absent from island-state dynamics.

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cond-mat.mes-hall 2026-05-08

Nonlinear Hall oscillations detect Brown-Zak fermion topology

Nonlinear Hall quantum oscillations to probe topological Brown-Zak fermions in graphene moir\'e systems

In graphene moiré systems the oscillations switch mechanisms with recurring Bloch states and expose quantum geometric control at fields down

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Due to the deep connection with the quantum geometry of electronic Bloch wavefunctions, the second-order nonlinear Hall effect (NLHE) has been an attractive topic since its proposal. However, studies on NLHE under a magnetic field have been lacking. Given that quantum oscillations in the linear response regime have been proven to be useful tools in investigating electronic systems, searching for quantum oscillations in NLHE is of great interest and is expected to provide new avenues to unveil rich quantum geometric properties of novel quasiparticles. Here, we propose a new type of NLHE quantum oscillations and experimentally probe it in graphene moir\'e systems. It stems from the alternation of the dominant NLHE mechanisms with recurring Bloch states under magnetic field, which enables sensitive detection of Brown-Zak fermions, giving an onset field as low as 0.5 T. Most importantly, when the commensurability condition is satisfied, the nonlinear transport of Brown-Zak fermions is mainly governed by quantum geometric contributions. Our findings not only establish a new type of quantum oscillations, but also demonstrate the first experimental detection of the topological nature of Brown-Zak fermions, shedding light on the exploration of novel topological quasiparticles.

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cond-mat.mes-hall 2026-05-08

Graphene Bernstein modes obey inter-harmonic ratios near m/n

Inter-harmonic ratio structure and saturation of Bernstein modes in graphene

Shared momentum sampling at fixed frequency cancels launch and screening factors, connecting low-power amplitudes to distinct saturation for

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Bernstein modes (BM) in graphene are finite-wavevector magnetoplasmons excited by contact near fields, whereas ordinary cyclotron resonance (CR) probes $q\approx0$. We derive the BM peak absorption in the quasiclassical ballistic regime and show that it factorizes into a launch spectrum, Bernstein-mode splitting, turning-point enhancement, and residual dielectric-response factor. At fixed excitation frequency, BM overtones ($n\ge2$) are sampled, to leading order, at the same momentum $q\simeq\omega/v_F$. Smooth launch and screening factors therefore cancel in inter-harmonic peak ratios, yielding $I_n/I_m\simeq m/n$, modified by linewidth corrections and one residual response ratio for each harmonic pair. In smooth-launcher synthetic tests, noisy full-$q$ spectra recover the residual ratio within errors: moderate launcher/dielectric misspecification within this benchmark family shifts it by only $\sim\!1$--$2\%$, whereas linewidth assumptions shift it by $\sim\!10$--$30\%$. The same factorization connects low-power amplitudes to nonlinear saturation. If BM harmonics share the same cooling region and bolometric readout, the low-power slope times onset intensity is harmonic independent, while BM and CR power sweeps obey distinct normalized saturation curves with linewidth scalings $\Gamma^{-1/2}$ and $\Gamma^{-1}$.

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cond-mat.mes-hall 2026-05-08 2 theorems

Wave packet motion reads out Dirac point winding numbers

Dynamically Characterizing the Structures of Dirac Points via Wave Packets

Center-of-mass drift and spin texture encode winding numbers at Dirac and parabolic points in extended graphene.

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Topological non-trivial band structures are the core problem in the field of topological materials. In this paper, we investigate the topological band structure in a system with controllable Dirac points from the perspective of wave packet dynamics. By adding a third-nearest-neighboring coupling to the graphene model, additional pairs of Dirac points emerge. The emergence and annihilation of Dirac points result in hybrid and parabolic points, and we show that these band structures can be revealed by the dynamical behaviors of wave packets. Particularly, for the gapped hybrid point, the motion of the wave packet shows a one-dimensional \emph{Zitterbewegung} motion. Furthermore, we also show that the winding number associated with the Dirac point and parabolic point can be determined via the center-of-mass and spin texture of wave packets, respectively. The results of this work could motivate new experimental methods to characterize the system's topological signatures through wave packet dynamics, which may also find application in systems of other exotic topological materials.

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cond-mat.mes-hall 2026-05-08

Spin and charge waves persist in one-nanometer WSe2 segments

Collective quantum state at the atomic limit

Ultrashort boundary segments act as collective-mode quantum dots whose excitations couple differently than single-particle states.

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Collective quantum states are often associated with extended systems, where spatially extensive degrees of freedom enable emergent many-body behavior; whether such strongly correlated states survive at atomic dimensions remains a fundamental question. Tomonaga-Luttinger liquids provide a paradigmatic example of one-dimensional collective quantum matter characterized by spin-charge separation. Using low-temperature scanning tunneling microscopy and spectroscopy, we directly visualize quantized collective modes in atomically confined mirror twin boundary segments of monolayer WSe2. Distinct standing-wave branches associated with fractionalized spin and charge excitations persist in segments as short as one nanometer, establishing the atomic-scale confinement limit of Luttinger-liquid behavior. These ultrashort segments form a new class of many-body quantum dots whose discrete spectra arise from confined collective bosonic modes rather than single-particle electron states. When assembled into ordered chains, inter-dot coupling reshapes electron-like fundamental states while collective spin/charge excitations remain largely intact, revealing distinct coupling responses of emergent many-body modes. Our results demonstrate that collective quantum matter can persist and exhibit fundamentally distinct coupling behavior at atomic length scales, establishing a novel platform for engineering strongly correlated quantum phases from atomically confined building blocks.

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cond-mat.mes-hall 2026-05-08

Two-frequency cavity modulation creates new magnon-polariton anticrossings

Multifrequency Floquet Engineering of Magnon Polaritons

Commensurate drives produce spectrum features absent in single-frequency cases, offering flexible control over hybrid energy levels.

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Floquet engineering of cavity magnon-polaritons by periodically modulating the magnon frequency has recently attracted much interest as a way to manipulate the energy spectrum of magnon-photon hybrid systems. However, modulating the frequency of magnons by a time-varying bias magnetic field can be challenging. We demonstrate cavity magnon-polariton Floquet engineering by modulating the microwave cavity frequency, allowing large modulation depth and bandwidth. We apply commensurate two-frequency Floquet modulations with the higher frequency at twice and three times the lower frequency, and demonstrate that the resulting spectrum depends on the relative amplitude and phase of the two drive tones. In comparison with single-frequency Floquet modulations, the spectrum has qualitatively different features; in particular, new anticrossings appear between previously uncoupled sidebands. Our platform offers an alternative way to manipulate Floquet quasi-energy levels in hybrid systems.

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cond-mat.mes-hall 2026-05-08

Electric field tunes electron localization in MoSe2/WS2 moiré lattice

Tunable Interlayer Charge-transfer States in MoSe₂/WS₂ Moir\'e Superlattices

Vertical field switches band alignment, creates tunable charge-transfer band on honeycomb lattice, and predicts charge-ordered states at all

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Moir\'e superlattices formed by transition metal dichalcogenide (TMD) heterobilayers provide a versatile platform for studying strongly correlated electronic, excitonic, and topological phenomena in solids. In particular, angle-aligned MoSe$_2$/WS$_2$ heterobilayers, which have a Type-I band alignment at zero vertical electric field, host rich correlated spin and charge physics. Here, combining large-scale first-principles calculations and optical reflection spectroscopy, we report a thorough study of the emergent moir\'e excitonic states and interlayer charge-transfer states in angle-aligned electron-doped MoSe$_2$/WS$_2$ moir\'e superlattices. The moir\'e excitonic states serve as sensitive optical probes to the localization profile of doped electrons. We observe a series of interlayer charge-transfer transitions from n/n$_0$ = 1 to 4 (where n$_0$ denotes the moir\'e density) when the vertical electric field switches the heterostructure band alignment from Type-I to Type-II. By tuning the vertical electric field, we can precisely control the interlayer electron localization, realizing a Fermi-Hubbard model with a tunable charge-transfer band on an effective honeycomb lattice. Furthermore, Monte Carlo simulation of the doping dependence of the electric-field susceptibility predicts that multiple correlated charge-ordered states appear at both integer and fractional fillings. Our results provide a holistic understanding of the emergent optical excitations and the correlated charge-transfer states in electron-doped MoSe$_2$/WS$_2$ moir\'e superlattices.

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cond-mat.mes-hall 2026-05-07

Collinear magnets host mixed-parity altermagnetism

Mixed-Parity Altermagnetism in Collinear Spin-Orbital Magnets

Zero-magnetization antiferromagnets show spin splitting neither even nor odd when antiparallel sectors share a mirror symmetry in 2D.

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Altermagnetism has so far mainly been understood in its even- and odd-parity forms. We show that collinear antiferromagnets with zero net magnetization can also host mixed-parity spin splitting, namely neither purely even nor purely odd in momentum. We identify the symmetry conditions for such mixed-parity altermagnetism and show that, in two dimensions, it can arise in spin-orbital magnets when the two antiparallel spin sectors are related by a single mirror symmetry. Using a two-sublattice two-orbital model, we demonstrate that circularly polarized light induces mixed-parity altermagnetism at finite staggered potential and odd-parity spin-orbital altermagnetism at zero staggered potential. Mixed-parity altermagnetism thereby emerges as the intermediate spin-split regime between even- and odd-parity altermagnetism when spin splitting and zero net magnetization are maintained. Spin-resolved orbital Edelstein effects provide a complementary electrical probe of the underlying spin-orbital order.

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cond-mat.mes-hall 2026-05-07

Gate field bends valence band into M shape while flattening conduction band in rhombo

Field-induced asymmetric band flattening and ideal quantum geometry in rhombohedral graphene

This asymmetric evolution produces near-ideal quantum geometry that supports topological phases only under electron doping at large fields.

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Rhombohedral graphene exhibits an exceptionally diverse array of correlated phases that depend sensitively on the displacement field. Compiling reported phases into a unified phase diagram reveals a pronounced field-dependent electron-hole asymmetry: correlated states on the hole-doped side emerge at small displacement fields, whereas the fractional quantum anomalous Hall effect (FQAHE) is observed exclusively on the electron-doped side under large displacement fields. This stark asymmetry highlights the need to understand how flat bands evolve with displacement fields. Here, we directly visualize the field-induced electron-hole asymmetric band flattening in rhombohedral pentalayer graphene (R5G) using nanospot angle-resolved photoemission spectroscopy with electrostatic gating. Beyond gap opening and spectral weight redistribution indicative of layer polarization, the gating field drives a strongly asymmetric modification of the flat bands: the flat valence band (FVB) evolves into an M-shaped dispersion at high field, whereas the flat conduction band (FCB) progressively flattens with increasing field. Comparison with calculations identifies critical parameters governing the band curvature of R5G, from which the resulting finite Berry curvature and near-ideal quantum geometry support the emergence of topological phases under electron doping at large fields. These results establish a direct link between the asymmetric phase diagram, band structure evolution, and quantum geometry, providing a microscopic framework for understanding correlated and topological phases in rhombohedral graphene.

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cond-mat.mes-hall 2026-05-07 Recognition

TMD interfaces tune Rashba splitting for stronger THz emission

Rashba engineering at van der Waals interfaces

Stacking different monolayers produces in-gap states whose spin-orbit coupling exceeds bulk TMD conversion efficiency.

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Two-dimensional transition metal dichalcogenide (TMD) interfaces offer a versatile platform for studying emergent quantum phenomena and enabling novel device functionalities. When distinct TMD monolayers are stacked vertically or laterally stitched, their interfaces can exhibit unique electronic band alignments, giving rise to long-lived interlayer excitons, charge transfer effects, and moir\'e superlattices with correlated states. Here, we demonstrate that the interface between a large variety of two different epitaxially grown TMD monolayers controls the intensity and sign of the Rashba spin splitting, which is probed using THz spintronic emission. Optimized TMD heterobilayers, such as HfSe$_2$/PtSe$_2$, show enhanced THz emission that surpass the spin-to-charge conversion efficiency of bulk TMDs, confirming the presence of Rashba states with large spin splitting at the interface. By combining spin- and angle-resolved photoemission spectroscopy with density functional theory, we reveal that the electronic hybridization between the two different TMD monolayers gives rise to extended in-gap states with strong Rashba spin-orbit coupling. The choice of TMD layers enables to engineer the sign and strength of spin-to-charge conversion in van der Waals heterobilayers opening up perspectives to build efficient and tunable THz spintronic emitters.

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cond-mat.mes-hall 2026-05-07

Curved nanopyramids create spin-wave band gaps in continuous films

Sculpting Spin-Wave Landscapes via Curvature of 2D Magnonic Crystals

Permalloy films on 400-nm pyramid arrays show tunable gaps and valley-localized modes through modified demagnetizing fields.

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Engineering the dispersion relation is one of the key ingredients enabling the application of spin waves in computational elements. One way to engineer the spin-wave band structure is to create an artificial magnonic crystal, which can be used to design specific band gaps or dispersion branches. However, creating a two-dimensional magnonic crystal usually requires removing material, which dramatically decreases the decay lengths of spin waves. Here, we present a method to manipulate the demagnetizing field landscape by utilizing large-area curvilinear nanotemplates consisting of three-dimensional nanopyramids arranged in a square lattice with a period of 400 nm. In a 50-nm-thick Permalloy film grown on these curvilinear templates, we experimentally observe a complete in-plane band gap together with flat-band modes that exhibit strong real-space localization of the spin waves in the pyramid valleys. Micro-focused Brillouin light scattering measurements corroborate the numerically predicted dispersion and reveal the possibility of opening and closing this gap by varying the external magnetic field. Our results establish three-dimensional-templated continuous films as a versatile platform for two-dimensional signal processing and magnonic computing elements.

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cond-mat.mes-hall 2026-05-07

Vacancy symmetry decides band-gap opening in graphene superlattices

Guidelines for band gap opening in graphene superlattices with periodic {π}-vacancy distribution

C3 motifs and mirror-preserving C2 motifs pin Dirac cones at Γ after 3n folding; absent mirrors allow off-center shifts and gap closure.

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Periodic $\pi$-vacancies in graphene superlattices (GSLs) provide a symmetry-based route to band-gap opening in graphene by modifying the $\pi$-band dispersion. However, the symmetry conditions that determine whether a vacancy motif can open a band gap remain unclear. Here, we investigate periodic $\pi$-vacancy GSLs using a nearest-neighbor tight-binding model with one $p_z$ orbital per carbon site to identify the symmetry requirements for gap opening. $\pi$-vacancies, representing functionalized, substituted, or missing carbon sites, are modeled as site deletions in the $\pi$ basis, with all hopping matrix elements to and from the deleted sites set to zero. We focus on $\pi$-vacancy motifs with $C_2$ and $C_3$ point-group symmetry. A $3n \times 3n$ GSL, where $n=1,2,3,\ldots$ is the integer scaling factor multiplying the honeycomb primitive-cell vectors, folds $K$ and $K'$ to $\Gamma$ and can therefore open a band gap. For $C_3$-type vacancies, the Dirac cones remain pinned at high-symmetry points and thus stay at $\Gamma$ in folded $3n$ GSLs. In contrast, $C_2$-type vacancies that reduce the global point group of the GSL to $D_{2h}$ by preserving a pair of perpendicular mirror symmetries, $\sigma_v \perp \sigma_d$, can also constrain the Dirac cones to $\Gamma$. When the $\sigma_v$ and $\sigma_d$ mirror planes are absent, the cones are allowed to shift away from $\Gamma$ to $(\pm \Delta q,\pm \Delta q)$ in the $3n$ superlattice.

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cond-mat.mes-hall 2026-05-07

Magnetic fields brighten spin-polarized edge modes at atomic steps

Magnetic Brightening and Nanoscale Imaging of Spin-Polarized Helical Edge Modes

Near-field infrared signals scale linearly with layer number, showing preserved helical conduction at 100 meV energies unlike DC transport.

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Efficient sub-10 nm electric transport remains a major challenge for nanoelectronics due to high losses and impedance mismatches in conventional Drude metals. Despite their promise of dissipationless, reflection-free conduction, topologically protected chiral edge modes remain little explored in their nanoscale spin polarized transport-particularly regarding real-space visualization, magnetic field tunability, and high-frequency edge conductivity. Here, we report magnetic brightening and nanoscale visualization of highly spin-polarizable infrared helical edge states using cryogenic magneto-infrared scattering-type scanning near-field optical microscopy (cm-IR-sSNOM). Our measurements reveal magnetic field-induced near-field conductivity at step edges, uncovering quantum spin Hall spin-splitting modes with enhanced infrared polarizability and slightly narrowed near-field profiles. In addition, the infrared edge electrodynamic response scales nearly linearly with atomic layer number, providing compelling evidence that magnetic-field-induced gaps do not disrupt individual-layer edge states at energies of around 100 meV. These results sharply contrast with microwave and DC transport, where even small magnetically induced gaps decrease edge conduction. Magnetically tunable, topologically robust high-frequency edge modes open a pathway toward ultralow-loss nanoscale interconnects and quantum logic architectures for next-generation microelectronics, spintronics and quantum information science.

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cond-mat.mes-hall 2026-05-07

Nanodisks hybridize modes to create tunable spin-wave bandgaps

Spin-wave bandgap engineering via mode hybridization in dipolar-coupled YIG film/CoFeB nanodisk magnonic crystals

In YIG-CoFeB structures, gaps open from mixing with nanodisk-induced standing modes, controllable by geometry and magnetization state.

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We investigate spin-wave transport in hybrid two-dimensional magnonic crystals comprising a low-damping yttrium iron garnet (YIG) film coupled to a periodic array of CoFeB nanodisks. Using propagating spin-wave spectroscopy, super-Nyquist magneto-optical Kerr effect microscopy, and micromagnetic simulations, we demonstrate the formation of pronounced and tunable bandgaps that do not originate from conventional Bragg scattering. Instead, these gaps arise from hybridization between the fundamental magnonic-crystal mode and in-plane transverse standing modes induced by the periodic nanodisk array. The spectral position and width of these gaps are controlled by geometric parameters and by the magnetic state of the nanodisks, including their vortex configuration, which governs both static and dynamic dipolar coupling. For larger lattice periods, additional gaps emerge through hybridization with modes quantized both transverse and parallel to the spin-wave propagation direction, reflecting dispersion folding in two dimensions. Our results establish mode hybridization as a versatile mechanism for engineering spin-wave band structures beyond the constraints of Bragg scattering and provide a pathway toward reconfigurable magnonic devices based on dipolar-coupled hybrid architectures.

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cond-mat.mes-hall 2026-05-07

Coherence leaves thermodynamic efficiency bounds intact

Quantum Coherence Reshapes Thermodynamic Bounds for Thermal Machines

Two-terminal quantum conductors obey classical TUR limits on performance even when coherent transport dominates at finite power.

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Thermodynamic Uncertainty Relations (TURs) set universal bounds linking current fluctuations to entropy production in nonequilibrium steady states. Their multidimensional generalization (MTUR) introduces matrix inequalities connecting current covariances and mean values. We analyze these bounds in a paradigmatic quantum thermal device, a two-terminal conductor, operating as a heat engine, refrigerator, or heat pump. We show that classical performance limits on efficiency and coefficient of performance remain constrained by the TUR when finite power or heat flow from cold to hot reservoirs is maintained, even in regimes dominated by coherent transport. We further identify the conditions that optimize TUR and MTUR violations, demonstrating that cross-correlations can enhance the joint precision of charge and heat currents near the linear-response regime.

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cond-mat.mes-hall 2026-05-07 3 theorems

Orbital-magnon conversion switches magnets at room temperature

Giant orbital-magnon conversion driven perpendicular magnetization switching

A metal-antiferromagnet bilayer converts orbital momentum to magnons over ten times more efficiently, enabling perpendicular switching in Co

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The pursuit of beyond-Moore information technologies has stimulated the exploration of novel information carriers, such as electron spin, orbital, and magnon, beyond electron charge. Efficient interconversion among these degrees of freedom and precise control over the information states are crucial for advancing nanoelectronic devices. However, a direct coupling between orbital angular momentum (L) and magnons (M) has remained elusive, and magnetization switching through orbital-to-magnon (L-M) conversion has not yet been achieved. Here, we report the experimental demonstration of L-M conversion in an orbital metal/antiferromagnetic insulator bilayer at room temperature, with an efficiency over an order of magnitude higher than that in traditional orbital systems lacking the L-M process. Consequently, we achieved efficient room-temperature perpendicular magnetization switching in a CoFeB ferromagnetic layer mediated by this new mechanism. Our findings establish a direct link between orbitronics and magnonics, providing a new platform for the development of advanced nano-devices based on orbital-driven magnonic phenomena.

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cond-mat.mes-hall 2026-05-07 Recognition

Asymmetric-hopping model captures bulk steady state under current

Construction and Analysis of the Effective Model for the Bulk Steady State under Current in Boundary-Driven Open Systems

Effective temperature rises linearly with current density, allowing separation of intrinsic effects from heating.

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Current-induced phenomena are often obscured by Joule heating, and their steady states are difficult to analyze in large open systems. We introduce a translationally invariant asymmetric-hopping model as an effective bulk description of boundary-driven systems under current. In a minimal case, it corresponds to an open-system Hatano--Nelson model. We find that the effective temperature rises linearly with current density, as observed experimentally. The model provides a useful tool for separating intrinsic current-induced effects from heating.

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cond-mat.mes-hall 2026-05-07 3 theorems

LC circuit turns Landau levels into Kitaev chain

Kitaev chain in synthetic dimension with cavity-controlled Majorana modes

Angular-momentum states in a 2D electron gas form a tunable topological superconductor whose Majorana modes are read and controlled by the腔.

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We introduce a tunable synthetic-dimension platform for realizing Kitaev-chain physics with high degree of control over Majorana zero modes. It is based on a generic Landau-quantized two dimensional electron system coupled to the magnetic flux of a superconducting LC circuit. The structured vector potential of a superconducting LC inductor induces attractive interactions between electron angular-momentum states at the lowest Landau level. These states serve as a synthetic dimension for the coveted fermionic Kitaev chain, with Majorana zero modes existing at the boundaries of the angular-momentum lattice. The crucial advantage of this proposal is the possibility of a robust, nonlocal readout and control of the Majorana states by a LC resonator. The platform relies on mature circuit QED and semiconductor technologies and provides a promising pathway to topological quantum computing.

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