Anisotropic paramagnetic response of topological Majorana surface states in the superconductor $\text{UTe}_2$

TL;DR

This paper investigates the anisotropic magnetic response of Majorana surface states in the superconductor UTe2, proposing magnetic measurements as a way to detect topological Majorana states through their unique spin susceptibility signatures.

Contribution

It provides a theoretical analysis of the anisotropic spin susceptibility of Majorana surface states in UTe2, highlighting their potential as experimental signatures of topological superconductivity.

Findings

Majorana surface states cause Ising-like anisotropy in spin susceptibility.

Surface spin susceptibility shows anomalous enhancement due to Majorana states.

Crystalline symmetry protects the Majorana surface states, influencing their magnetic response.

Abstract

Identifying the superconducting gap symmetry and topological signatures in the putative spin-triplet superconductor $\text{UTe}_2$ is an important issue. Especially, a smoking-gun detection scheme for Majorana surface states hallmarking topological superconductivity in $\text{UTe}_2$ is still lacking. In this study, we examine the surface spin susceptibility of $\text{UTe}_2$ with a particular focus on the contribution of the surface states. We find that Majorana surface states contribute significantly to the surface spin susceptibility, and give rise to an Ising-like anisotropy and anomalous enhancement in the surface spin susceptibility. We calculate the surface spin susceptibility as well as the local density of states using the recursive Green's function method and examine the anisotropy of the surface spin susceptibility in terms of the topological surface states and symmetry for all irreducible representations of odd-parity pairing states. Our results indicate that the Ising anisotropy and the anomalous enhancement are attributed to the Majorana surface state protected by the crystalline symmetry. These findings suggest the possibility of detecting the Majorana surface state via magnetic measurements.