Quasiparticle Interference of Spin-Triplet Superconductors: Application to UTe$_2$

Abstract

Quasiparticle interference (QPI) obtained from scanning tunneling microscopy (STM) is a powerful method to help extract the pairing symmetry of unconventional superconductors. We examine the general properties of QPI on surfaces of spin-triplet superconductors, where the properties of the $\vec d$-vector order parameter and topological surface bound states offer important differences from QPI on spin-singlet superconducting materials. We then apply the theory to a model specific to UTe$_2$, and compare the resulting QPI with recent STM measurements. We conclude that the two candidate Cooper pair instabilities $B_{2u}$ and $B_{3u}$ exhibit distinct features in the QPI intensity to discriminate these using the experimental data. Characteristic features of the emergent topological surface states protected by chiral symmetry in general, and by mirror symmetries in the case of UTe$_2$, provide further unique signatures to help pinpointing the pairing symmetry channel in this material.