Unconventional superconductivity protected from disorder on the kagome lattice
Sofie Castro Holbæk, Morten H. Christensen, Andreas Kreisel, Brian M. Andersen
Abstract
Motivated by the recent discovery of superconductivity in the kagome ${A\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ $(A=\mathrm{K}, \mathrm{Rb}, \mathrm{Cs})$ 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 quasiparticle 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.