Pair Wavefunction Symmetry in UTe2 from Zero-Energy Surface State Visualization

TL;DR

This study uses surface state visualization to investigate the superconducting order parameter in UTe2, providing evidence that it is a non-chiral state, likely B3u, through zero-energy Andreev tunneling observations.

Contribution

It demonstrates the use of zero-energy surface state imaging and Andreev tunneling to identify the symmetry of the superconducting order parameter in UTe2.

Findings

Zero-energy Andreev conductance observed at UTe2 surface.

Surface imaging indicates non-chiral superconducting state.

Most consistent state is B3u based on scattering analysis.

Abstract

Although nodal spin-triplet topological superconductivity appears probable in UTe2, its superconductive order-parameter $\Delta_k$ remains unestablished. In theory, a distinctive identifier would be the existence of a superconductive topological surface band (TSB), which could facilitate zero-energy Andreev tunneling to an s-wave superconductor, and also distinguish a chiral from non-chiral $\Delta_k$ via enhanced s-wave proximity. Here we employ s-wave superconductive scan-tips and detect intense zero-energy Andreev conductance at the UTe2 (0-11) termination surface. Imaging reveals sub-gap quasiparticle scattering interference signatures with a-axis orientation. The observed zero-energy Andreev peak splitting with enhanced s-wave proximity, signifies that $\Delta_k$ of UTe2 is a non-chiral state: B1u, B2u or B3u. However, if the quasiparticle scattering along the a-axis is internodal, then a non-chiral B3u state is the most consistent for UTe2.