Spatially anisotropic Kondo resonance coupled with the superconducting gap in a kagome metal

Haitao Yang; Hao Zhang; Hong-Jun Gao; Hui Chen; Ruwen Wang; Wei Ji; Zhen Zhao; Zhongqin Zhang; Zichen Huang; Ziqiang Wang

arxiv: 2502.20735 · v3 · submitted 2025-02-28 · ❄️ cond-mat.supr-con

Spatially anisotropic Kondo resonance coupled with the superconducting gap in a kagome metal

Zichen Huang , Hui Chen , Zhongqin Zhang , Hao Zhang , Zhen Zhao , Ruwen Wang , Haitao Yang , Wei Ji

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Ziqiang Wang Hong-Jun Gao

This is my paper

Pith reviewed 2026-05-23 02:26 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con

keywords kagome metalKondo resonancesuperconducting gapCr impuritiesCsV3Sb5anisotropic patternssuperfluid densitycharge density wave

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The pith

Dilute Cr impurities in CsV3Sb5 create anisotropic Kondo resonances that enhance the superconducting gap by engaging non-superconducting carriers.

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

The paper establishes that magnetic Cr impurities added to the kagome superconductor CsV3Sb5 generate local moments and produce Kondo resonances. These resonances appear as ripple-like anisotropic patterns around each Cr site and break all local mirror symmetries while weakening the charge density wave. With the onset of Kondo screening the superconducting coherence peaks grow taller and the gap deepens, even while retaining finite zero-energy conductance. A sympathetic reader cares because the result points to a mechanism in which non-superconducting carriers at the Fermi surface screen the moments and simultaneously raise the superfluid density.

Core claim

With the emergence of Kondo screening, the coherence peak and depth of superconducting gap with finite zero-energy conductance are enhanced. This suggests that non superconducting carriers at the Fermi surface in the parent compound participate in the Kondo effect, simultaneously screening Cr magnetic moments and increasing the superfluid density.

What carries the argument

Spatially anisotropic Kondo resonance around individual Cr atoms, forming ripple-like patterns that break local mirror symmetries and intertwine with the superconducting gap.

If this is right

Dilute Cr impurities weaken long-range charge density wave order.
Local Cr moments produce Kondo resonances with anisotropic spatial patterns.
Kondo screening increases the superfluid density through participation of non-superconducting carriers.
The anisotropic Kondo resonance couples directly to the superconducting gap while preserving finite zero-energy conductance.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Varying Cr concentration could map how the fraction of participating carriers scales with impurity density.
The same screening mechanism may operate in other kagome compounds where local moments coexist with superconductivity.
Pressure-tuned versions of CsCr3Sb5 might show analogous carrier redistribution if Kondo physics persists.

Load-bearing premise

The observed enhancement of the superconducting gap is produced by non-superconducting carriers joining the Kondo screening rather than by other impurity-induced changes such as modified scattering rates or altered band filling.

What would settle it

Quantitative modeling or measurements that attribute the gap deepening to scattering-rate changes alone, or that show the enhancement persisting when Kondo signatures are absent, would falsify the carrier-participation claim.

Figures

Figures reproduced from arXiv: 2502.20735 by Haitao Yang, Hao Zhang, Hong-Jun Gao, Hui Chen, Ruwen Wang, Wei Ji, Zhen Zhao, Zhongqin Zhang, Zichen Huang, Ziqiang Wang.

**Figure 4.** Figure 4: DFT calculations of spin density distribution around a Cr dopant in CsV3Sb5. a, Fully relaxed atomic structure model of the V-Sb kagome layer after a V atom is substituted by a Cr atom. b, Zoom-in of the blue dashed region in a. Green dashed lines indicate Cr-V bonds, with bond lengths labeled. The blue and orange dashed lines in a,b represent the mirror planes for mirror symmetry operations Mx and My. If … view at source ↗

read the original abstract

The chromium-based kagome metal CsCr3Sb5 has garnered significant interest due to its strong electron correlations, intertwined orders and potential for unconventional superconductivity under high pressure. The evolution of magnetic and superconducting interactions as the more frequently studied CsV3Sb5 is doped to CsCr3Sb5 remains poorly understood. Here, we demonstrate the emergence of a spatially anisotropic Kondo resonance intertwined with the superconducting gap, enabled by introducing magnetic Cr impurities into the kagome superconductor CsV3Sb5. The addition of dilute Cr impurities not only weakens long range charge density wave order but also produces local magnetic moments that leads to Kondo resonances. We show that the Kondo resonance forms anisotropic, ripple like spatial patterns around individual Cr atoms, breaking all local mirror symmetries. We further reveal that with the emergence of Kondo screening, the coherence peak and depth of superconducting gap with finite zero-energy conductance are enhanced. This suggests that non superconducting carriers at the Fermi surface in the parent compound participate in the Kondo effect, simultaneously screening Cr magnetic moments and increasing the superfluid density. Our findings offer an opportunity to study the interplay between superconductivity and local magnetism in kagome materials.

Editorial analysis

A structured set of objections, weighed in public.

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.

Desk Editor's Note private letter to a colleague

STM data show anisotropic Kondo resonances around Cr in CsV3Sb5 plus gap enhancement, but the proposed link to non-SC carriers raising superfluid density lacks modeling to exclude scattering or doping shifts.

read the letter

The main takeaway is that this paper presents STM spectra from dilute Cr-doped CsV3Sb5 in which Kondo resonances appear with strong spatial anisotropy around the impurity sites, breaking local mirror symmetry, and the superconducting coherence peaks grow taller while the gap deepens with finite zero-bias conductance. The authors tie this to Kondo screening of Cr moments by carriers that were not superconducting in the parent compound, thereby increasing superfluid density. That combination of local anisotropy and gap change is the concrete result worth noting first. The work maps the suppression of long-range CDW order and the emergence of ripple-like Kondo patterns, which is a clear experimental step forward in this kagome system. The spatial resolution and the direct comparison of spectra with and without the Kondo feature are useful additions to the existing literature on CsV3Sb5 doping. The data themselves look like honest local-probe measurements that other groups can check against their own STM results. The soft spot sits in the interpretation. The claim that the gap enhancement arises specifically because non-superconducting Fermi-surface carriers join the Kondo cloud is stated without any calculation that tests it against simpler alternatives, such as Cr-induced pair-breaking scattering that changes the gap edge or rigid-band shifts from substitution that alter the density of states. No BdG or T-matrix modeling appears to quantify the link between the anisotropic resonance and the uniform gap change. The stress-test note correctly flags this gap. The paper is aimed at researchers already working on intertwined orders in AV3Sb5 compounds and on local magnetism in superconductors. Someone running STM on related kagome materials would get value from the raw spectra and the anisotropy maps even if the mechanism discussion stays provisional. It deserves peer review because the experimental observations are specific enough to merit referee scrutiny on the data quality and any additional analysis in the full text, though the authors should expect requests for more quantitative support on the mechanism.

Referee Report

2 major / 2 minor

Summary. The manuscript reports STM measurements on dilute Cr-doped CsV3Sb5, observing spatially anisotropic Kondo resonances around individual Cr atoms that break local mirror symmetries and weaken the CDW order. It further claims that the emergence of Kondo screening enhances the superconducting coherence peaks and deepens the gap (while retaining finite zero-bias conductance), interpreting this as evidence that non-superconducting Fermi-surface carriers in the parent compound join the Kondo screening cloud, thereby screening Cr moments and increasing superfluid density.

Significance. If substantiated, the work would provide experimental evidence for an unusual interplay in which local magnetic moments and Kondo screening can enhance rather than suppress superconductivity in a kagome metal. The reported spatial anisotropy of the Kondo resonance is a concrete observational result. The interpretive link to increased superfluid density, however, rests on an unmodeled assumption and therefore limits the current significance of the central claim.

major comments (2)

[Abstract and Discussion] Abstract and Discussion: The suggestion that the observed gap enhancement arises because 'non superconducting carriers at the Fermi surface in the parent compound participate in the Kondo effect, simultaneously screening Cr magnetic moments and increasing the superfluid density' is stated without any quantitative modeling (e.g., self-consistent BdG+Kondo or T-matrix calculations) that distinguishes this mechanism from alternatives such as Cr-induced pair-breaking scattering or rigid-band chemical-potential shifts.
[Section 4] Section 4: The enhancement of coherence-peak height and gap depth is presented as direct evidence for increased superfluid density, yet the manuscript supplies no error analysis, concentration-dependent trends, or comparison spectra that would exclude impurity scattering rate changes as the origin of the spectral modifications.

minor comments (2)

The Cr concentration (or substitution level) is described only as 'dilute'; an explicit value or range should be stated in the abstract and methods.
Figure captions should include STM setpoint parameters (bias, current) and scale bars to allow direct comparison with other kagome STM studies.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thorough review and valuable comments on our manuscript. We address each major comment below and have made revisions to the manuscript where necessary to clarify our findings and interpretations.

read point-by-point responses

Referee: [Abstract and Discussion] The suggestion that the observed gap enhancement arises because 'non superconducting carriers at the Fermi surface in the parent compound participate in the Kondo effect, simultaneously screening Cr magnetic moments and increasing the superfluid density' is stated without any quantitative modeling (e.g., self-consistent BdG+Kondo or T-matrix calculations) that distinguishes this mechanism from alternatives such as Cr-induced pair-breaking scattering or rigid-band chemical-potential shifts.

Authors: We acknowledge that the manuscript does not include quantitative theoretical modeling to distinguish the proposed Kondo screening mechanism from alternatives. As an experimental STM study, our primary contribution is the observation of spatially anisotropic Kondo resonances and their correlation with enhanced superconducting gap features. The interpretation regarding non-superconducting carriers participating in Kondo screening is presented as a plausible explanation based on the data. We have revised the abstract and discussion to frame this more cautiously as a suggested mechanism, and added a note that detailed modeling would be valuable for future work to differentiate it from other possibilities such as scattering effects or band shifts. revision: partial
Referee: [Section 4] The enhancement of coherence-peak height and gap depth is presented as direct evidence for increased superfluid density, yet the manuscript supplies no error analysis, concentration-dependent trends, or comparison spectra that would exclude impurity scattering rate changes as the origin of the spectral modifications.

Authors: We agree that additional statistical analysis would strengthen the presentation. In the revised manuscript, we have included error estimates on the measured coherence peak heights and gap depths from multiple spectra. We have also added a discussion explaining why changes in impurity scattering rates are unlikely to account for the observed enhancements, given the anisotropic spatial patterns and the specific enhancement of both peak height and gap depth. However, systematic concentration-dependent studies and direct comparisons to non-magnetic impurities would require additional experimental efforts beyond the current scope. revision: partial

Circularity Check

0 steps flagged

No circularity: experimental observation with interpretive suggestion only

full rationale

The paper reports STM measurements of Kondo resonances and superconducting gap features in Cr-doped CsV3Sb5. Its central statement is an observational suggestion ('This suggests that non superconducting carriers... participate in the Kondo effect'), not a derivation, equation, or fitted prediction. No self-citations, ansatze, or uniqueness theorems are invoked as load-bearing steps. The work contains no mathematical chain that reduces to its own inputs by construction and is therefore self-contained as an experimental report.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the domain assumption that STM spectra directly map Kondo resonances and that gap changes are attributable to carrier screening rather than other doping effects; no free parameters or invented entities are introduced in the abstract.

axioms (1)

domain assumption STM differential conductance faithfully reports the local density of states including Kondo and superconducting features
Standard assumption invoked when interpreting STM data on Kondo and superconducting systems.

pith-pipeline@v0.9.0 · 5765 in / 1183 out tokens · 41337 ms · 2026-05-23T02:26:14.472861+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

1 extracted references · 1 canonical work pages

[1]

1 Stewart, G. R. Unconventional superconductivity. Advances in Physics 66, 75-196 (2017). 2 Scalapino, D. J. A common thread: The pairing interaction for unconventional superconductors. Reviews of Modern Physics 84, 1383-1417 (2012). 3 Ran, S. et al. Nearly ferromagnetic spin-triplet superconductivity. Science 365, 684-687 (2019). 4 Ortiz, B. R. et al. Ne...

work page arXiv 2017

[1] [1]

1 Stewart, G. R. Unconventional superconductivity. Advances in Physics 66, 75-196 (2017). 2 Scalapino, D. J. A common thread: The pairing interaction for unconventional superconductors. Reviews of Modern Physics 84, 1383-1417 (2012). 3 Ran, S. et al. Nearly ferromagnetic spin-triplet superconductivity. Science 365, 684-687 (2019). 4 Ortiz, B. R. et al. Ne...

work page arXiv 2017