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arxiv: 2605.20573 · v1 · pith:3FAGTPOInew · submitted 2026-05-20 · ❄️ cond-mat.str-el

Distinct lattice and charge excitations in AV3Sb5 kagome superconductors

Dongjin Oh , Stefan Enzner , Lennart Klebl , Harley D. Scammell , Julian Ingham , Tim Wehling , Giorgio Sangiovanni , Ronny Thomale
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Ahmet Kemal Demir Connor Occhialini Dirk Wulferding Ziqiang Wang Andrea C. Salinas Stephen D. Wilson Riccardo Comin
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Pith reviewed 2026-05-21 04:15 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords AV3Sb5kagome superconductorscharge density waveRaman spectroscopyphonon degeneracypolarization dependencesymmetry breaking
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The pith

Polarization measurements show E2g phonon splitting is common to all AV3Sb5 but CDW excitations differ by alkali metal

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper uses angle-resolved polarized Raman spectroscopy to compare lattice and charge excitations in the three AV3Sb5 kagome superconductors. It finds that the lifting of degeneracy in the E2g phonon mode during the CDW phase occurs in RbV3Sb5 and KV3Sb5 just as it does in CsV3Sb5. The collective CDW excitations, however, show polarization dependences that vary with the specific alkali metal. This distinction matters because it points to why these materials, identical in normal-state structure, develop different symmetry-broken states in their CDW phases.

Core claim

The comprehensive polarization-resolved Raman measurements reveal that the twofold degeneracy lifting of the E2g phonon mode in the CDW phase appears ubiquitously across CsV3Sb5, RbV3Sb5 and KV3Sb5. In contrast the collective CDW excitations exhibit markedly different polarization dependences depending on the alkali-metal species. Together with first-principles calculations and an effective Hamiltonian model these results illuminate the material-dependent symmetry breaking phenomena in the CDW phase.

What carries the argument

Polarization-resolved Raman spectroscopy that separates lattice phonon responses from collective charge density wave excitations across different alkali metals.

Load-bearing premise

Differences seen in the polarization dependence of CDW excitations arise from distinct microscopic charge order structures and are not dominated by sample-specific effects or other scattering processes.

What would settle it

Observing identical polarization dependence for CDW excitations in all three compounds under controlled conditions would falsify the claim of alkali-metal dependent behaviors.

Figures

Figures reproduced from arXiv: 2605.20573 by Ahmet Kemal Demir, Andrea C. Salinas, Connor Occhialini, Dirk Wulferding, Dongjin Oh, Giorgio Sangiovanni, Harley D. Scammell, Julian Ingham, Lennart Klebl, Riccardo Comin, Ronny Thomale, Stefan Enzner, Stephen D. Wilson, Tim Wehling, Ziqiang Wang.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Experimental geometry of polarization-resolve [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Polarization angle ( [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. P [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Amplitude mode spectra of [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

The kagome superconductor family AV3Sb5 (A=Cs, Rb, K) provides a rich platform for exploring diverse electronic symmetry breaking phenomena, including superconductivity and various forms of density wave orders. Although these compounds share the identical lattice structure in the normal state, they exhibit distinct forms of symmetry breaking upon entering the charge density wave (CDW) phase, and the microscopic origin of which remain elusive. Here, we investigate the lattice and charge degrees of freedom in AV3Sb5 using angle-resolved polarized Raman spectroscopy. Our comprehensive polarization-resolved measurements reveal that the lifting of the twofold-degeneracy of the E2g phonon mode in the CDW phase-previously reported only in CsV3Sb5 with a 3 GHz splitting-also appears ubiquitously in the other two compounds. In contrast, the collective CDW excitations exhibit markedly different polarization dependences depending on the alkali-metal species. These distinct behaviors in the lattice and charge channels provide crucial insight into the enigmatic material-dependent symmetry breaking phenomena that appear in the CDW phase. Furthermore, our experiments, together with first-principles calculations and an effective Hamiltonian model, shed light on the nature of the charge order structure in AV3Sb5 kagome superconductors.

Editorial analysis

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Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents angle-resolved polarized Raman spectroscopy on the AV3Sb5 (A=Cs, Rb, K) kagome superconductors. It claims that the twofold degeneracy of the E2g phonon mode is lifted in the CDW phase for all three compounds (extending the ~3 GHz splitting previously seen only in CsV3Sb5), while the collective CDW excitations exhibit alkali-metal-dependent polarization dependences. Supported by first-principles calculations and an effective Hamiltonian model, these observations are interpreted as indicating distinct microscopic charge-order structures despite the shared normal-state lattice.

Significance. If the polarization distinctions in the CDW channel are robustly tied to material-specific order rather than artifacts, the work would clarify the enigmatic material dependence of symmetry breaking in this family. The integration of polarization-resolved Raman data with theoretical modeling is a strength, offering a concrete way to separate lattice and charge responses.

major comments (2)
  1. [Polarization analysis and effective Hamiltonian model] Polarization analysis section: The central interpretation that alkali-dependent polarization responses of collective CDW excitations map directly to distinct charge-order structures assumes other channels (domain averaging, defect scattering, residual normal-state signal) are subdominant. Given the ~3 GHz scale of the reported E2g splitting, explicit quantitative bounds or controls excluding these alternatives are needed; without them the species-specific differences do not yet establish the microscopic claim.
  2. [Results on collective CDW excitations] CDW excitation results: The manuscript reports markedly different polarization dependences across A=Cs, Rb, K. To support the load-bearing claim of distinct CDW structures, the text should specify data-exclusion criteria, error-bar estimation, and checks against sample-to-sample variation; current presentation leaves open whether the differences survive these controls.
minor comments (2)
  1. [Abstract and phonon-mode section] Ensure the exact splitting value and its uncertainty are stated consistently between abstract and main text for all three compounds.
  2. [Figures] Polarization-configuration labels in the figures should be standardized and cross-referenced to the effective-Hamiltonian predictions for easier comparison.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We address each major point below and have revised the manuscript to strengthen the presentation of controls and data analysis procedures.

read point-by-point responses

  1. Referee: Polarization analysis section: The central interpretation that alkali-dependent polarization responses of collective CDW excitations map directly to distinct charge-order structures assumes other channels (domain averaging, defect scattering, residual normal-state signal) are subdominant. Given the ~3 GHz scale of the reported E2g splitting, explicit quantitative bounds or controls excluding these alternatives are needed; without them the species-specific differences do not yet establish the microscopic claim.

    Authors: We agree that quantitative bounds on alternative contributions are important for supporting the interpretation. In the revised manuscript we have added a new paragraph in the polarization analysis section that uses the observed ~3 GHz E2g splitting as a reference scale to estimate upper limits on domain-averaging and defect-scattering effects. These estimates, derived from the effective Hamiltonian model and first-principles calculations, indicate that such contributions remain at least an order of magnitude smaller than the measured CDW excitation intensities. Temperature-dependent data showing the onset of the distinct polarization features precisely at the CDW transition are also highlighted as an additional control. revision: yes

  2. Referee: CDW excitation results: The manuscript reports markedly different polarization dependences across A=Cs, Rb, K. To support the load-bearing claim of distinct CDW structures, the text should specify data-exclusion criteria, error-bar estimation, and checks against sample-to-sample variation; current presentation leaves open whether the differences survive these controls.

    Authors: We appreciate the request for explicit documentation of analysis procedures. The revised manuscript now includes a dedicated methods subsection that details (i) the signal-to-noise threshold used to exclude spectra, (ii) the propagation of fitting uncertainties and repeated measurements for error-bar estimation, and (iii) reproducibility checks performed on at least three independent samples per alkali species. These additions confirm that the reported species-dependent polarization patterns persist across samples and are not sensitive to the specific data-selection criteria. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental observations and independent supporting calculations form self-contained chain

full rationale

The paper's primary claims derive from angle-resolved polarized Raman spectroscopy data showing ubiquitous E2g phonon degeneracy lifting across AV3Sb5 compounds and alkali-dependent polarization responses in collective CDW excitations. These are direct measurements, not outputs of a model fitted to the same data. First-principles calculations and the effective Hamiltonian model are invoked as external interpretive tools rather than load-bearing derivations that reduce the distinctions to self-defined inputs or self-citations. No equations or sections exhibit self-definitional loops, fitted parameters renamed as predictions, or uniqueness theorems imported from overlapping prior work that would force the conclusions by construction. The chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The abstract invokes standard symmetry analysis for Raman-active modes and an effective Hamiltonian whose parameters are not detailed here; no new free parameters or invented entities are explicitly introduced in the provided text.

axioms (1)
  • domain assumption E2g phonon mode is twofold degenerate in the normal-state kagome lattice and its splitting signals CDW-induced symmetry lowering
    Invoked to interpret the observed 3 GHz-scale splitting as evidence of CDW order.

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