Nonreciprocal impurity scattering as a probe for pairing symmetries in kagome superconductors

TL;DR

This paper proposes a method using impurity scattering patterns in scanning tunneling microscopy to distinguish between different superconducting pairing symmetries, especially TRSB and non-TRSB, in kagome superconductors.

Contribution

It introduces a theoretical approach to differentiate pairing symmetries via impurity-induced LDOS patterns, offering a new experimental probe for superconducting states.

Findings

Two magnetic impurities produce distinct LDOS patterns for different pairing symmetries.

TRSB pairing shows impurity scattering asymmetry, unlike non-TRSB pairing.

Distinct spectral features can be observed in STM experiments to identify pairing symmetry.

Abstract

The superconducting (SC) pairing symmetry and its link to time-reversal symmetry breaking (TRSB) in the vanadium-based kagome superconductors remain unresolved, with ambiguities stemming from sublattice interference and charge-density-wave (CDW) entanglement with superconductivity. Using two representative SC pairings, i.e., the conventional on-site $s$-wave and the TRSB $d_{x^2-y^2}+id_{xy}$-wave, as a model study, we theoretically show that while single magnetic impurity yield qualitatively identical spectral behavior of local density of states (LDOS) for these two symmetries, two magnetic impurities give rise to distinct LDOS patterns. For the conventional on-site $s$-wave pairing, time-reversal symmetry (TRS) enforces equivalent forward and backward scattering between two impurities across all impurity configurations, leading to near disappearance of a Yu-Shiba-Rusinov (YSR) state pair along the line connecting the two impurities. However, for the TRSB $d_{x^2-y^2}+id_{xy}$-wave pairing, this scattering equivalence holds only for inversion-symmetric impurity configurations, with a pair of YSR disappearance restricted to this case. These distinct spectral features are resolvable in scanning tunneling microscopy (STM) experiments, providing a direct avenue to discriminate TRSB and non-TRSB SC pairing symmetries in kagome superconductors and an alternative method to probe SC nonreciprocity that circumvents the ambiguities of conventional critical current-based techniques.