Symmetry-Broken Kondo Screening and Zero-Energy Mode in the Kagome Superconductor CsV3Sb5

TL;DR

This study visualizes impurity-induced quantum states in the kagome superconductor CsV3Sb5, revealing symmetry-breaking Kondo screening, zero-energy modes, and potential Majorana states, advancing understanding of topological and correlated phenomena in kagome materials.

Contribution

It uncovers unique impurity-induced phenomena in CsV3Sb5, including symmetry-breaking Kondo states and possible Majorana modes, highlighting novel quantum states in kagome superconductors.

Findings

Kondo resonance states observed near magnetic impurities.

Symmetry-breaking Kondo screening suggests electronic chirality.

Zero-bias conductance peaks indicate potential Majorana modes.

Abstract

The quantum states of matter reorganize themselves in response to defects, giving rise to emergent local excitations that imprint unique characteristics of the host states. While magnetic impurities are known to generate Kondo screening in a Fermi liquid and Yu-Shiba-Rusinov (YSR) states in a conventional superconductor, it remains unclear whether they can evoke distinct phenomena in the kagome superconductor AV3Sb5 (where A is K, Rb or Cs), which may host an orbital-antiferromagnetic charge density wave (CDW) state and an unconventional superconducting state driven by the convergence of topology, geometric frustration and electron correlations. In this work, we visualize the local density of states induced near various types of impurities in both the CDW and superconducting phases of CsV3-xMxSb5 (M = Ta, Cr) using scanning tunneling microscopy. We observe Kondo resonance states near magnetic Cr dopants. Notably, unlike in any known metal or CDW compound, the spatial pattern of Kondo screening breaks all in-plane mirror symmetries of the kagome lattice, suggesting an electronic chirality due to putative orbital loop currents. While Cooper pairs show relative insensitivity to nonmagnetic impurities, native V vacancies with weak magnetic moments induce a pronounced zero-bias conductance peak (ZBCP). This ZBCP coexists with trivial YSR states within the superconducting gap and does not split in energy with increasing tunneling transmission, tending instead to saturate. This behavior is reminiscent of signature of Majorana zero modes, which could be trapped by a sign-change boundary in the superconducting order parameter near a V vacancy, consistent with a surface topological superconducting state. Our findings provide a new approach to exploring novel quantum states on kagome lattices.