Unconventional superconductivity protected from disorder on the kagome lattice

TL;DR

This paper theoretically investigates how different types of unconventional superconductivity on the kagome lattice respond to disorder, revealing that spin-singlet states are surprisingly robust while spin-triplet states are fragile.

Contribution

It uncovers the disorder robustness of spin-singlet superconductivity on the kagome lattice due to sublattice effects, contrasting with the fragility of spin-triplet states.

Findings

Spin-singlet superconductivity is weakly pair-breaking despite sign changes.

Spin-triplet superconductivity remains fragile to disorder.

Disorder effects resemble conventional s-wave superconductors for singlet states.

Abstract

Motivated by the recent discovery of superconductivity in the kagome $A$V$_3$Sb$_5$ ($A$: K, Rb, Cs) metals, we perform a theoretical study of the symmetry-allowed superconducting orders on the two-dimensional kagome lattice with focus on their response to disorder. We uncover a qualitative difference between the robustness of intraband spin-singlet (even-parity) and spin-triplet (odd-parity) unconventional superconductivity to atomic-scale nonmagnetic disorder. Due to the particular sublattice character of the electronic states on the kagome lattice, disorder in spin-singlet superconducting phases is only weakly pair-breaking despite the fact that the gap structure features sign changes. By contrast, spin-triplet condensates remain fragile to disorder on the kagome lattice. We demonstrate these effects in terms of the absence of impurity bound states and an associated weak disorder-induced $T_c$-suppression for spin-singlet order. We also discuss the consequences for quasi-particle interference and their inherent tendency for momentum-space anisotropy due to sublattice effects on the kagome lattice. For unconventional kagome superconductors, our results imply that any allowed spin-singlet order, including for example $d+id$-wave superconductivity, exhibits a disorder-response qualitatively similar to standard conventional $s$-wave superconductors.