Speaker
Description
One of the central open questions in the heavy fermion triplet superconductor UTe₂ concerns the nature of the quasiparticles within the superconducting gap which make the gap unusually shallow. A compelling possibility is that the gap appears shallow because the nontrivial topology in UTe₂ gives rise to in-gap surface states. A persuasive proof of this would be the gapping of the in-gap surface states upon breaking the symmetry that protects the topological states.
In this talk I will discuss our recent vector magnetic-field scanning tunnelling microscopy studies of UTe$_2$. Atomic-scale spectroscopy reveals striking site-dependent superconductivity: Te sites host a large in-gap density of states that nearly fill the superconducting gap, whereas neighboring atomic sites remain gapped. We find that the application of a magnetic field suppresses the in-gap states on the Te sites, yielding a spatially homogeneous superconducting state with a markedly enhanced average gap depth relative to zero field. This site-selective gap deepening is in quantitative agreement with theoretical predictions for topological surface states in UTe$_2$ that possess dominant Te-orbital character within a point-nodal triplet superconducting state. Spectral-function calculations incorporating the Zeeman coupling reproduce the observed magnetic-field response. Our results provide direct spectroscopic evidence of the existence of topological surfaces in the superconducting phase of UTe$_2$ and establish this strongly correlated superconductor as a promising platform for exploring intrinsic topological superconductivity.