Topological surface states revealed by the Zeeman effect in superconducting UTe2

TL;DR

This study provides direct spectroscopic evidence of topological surface states in the superconductor UTe2 using magnetic-field scanning tunnelling microscopy, revealing site-dependent superconductivity and confirming theoretical predictions.

Contribution

First experimental identification of topological surface states in UTe2, demonstrating site-dependent superconductivity and magnetic-field response consistent with topological predictions.

Findings

Site-dependent in-gap states on Te sites in UTe2

Suppression of in-gap states under magnetic field on Te sites

Spectral calculations match experimental magnetic response

Abstract

Intrinsic topological superconductors with protected boundary modes obeying non-Abelian statistics constitute a vanishingly small class of quantum materials. A defining spectroscopic signature of such phases is the presence of in-gap topological surface states (TSS). However, despite extensive theoretical proposals, their unambiguous experimental identification has remained elusive. Here we use vector magnetic-field scanning tunnelling microscopy to obtain direct spectroscopic evidence of TSS in the spin-triplet superconductor UTe2. Atomic-scale spectroscopy reveals striking site-dependent superconductivity: Te sites host a large in-gap density of states that nearly fills the superconducting gap, whereas neighboring atomic sites remain gapped. Upon application of a magnetic field, the in-gap states on the Te sites are selectively suppressed, yielding a spatially homogeneous superconducting state with a markedly deeper gap relative to zero field. This site-selective gap evolution is in quantitative agreement with theoretical predictions for TSS in UTe2 that possess dominant Te-orbital character. Spectral-function calculations incorporating the Zeeman coupling reproduce the observed magnetic-field response. Our results provide a spectroscopic fingerprint of the long-sought TSS in superconductors and establish UTe2 as a compelling system for exploring intrinsic topological superconductivity.