Microscopic imaging homogeneous and single phase superfluid density in UTe$_2$

TL;DR

This study uses microscopic imaging to analyze the superfluid density in UTe$_2$, revealing homogeneous superfluid properties and supporting a dominant chiral superconducting order without evidence of multiple phase transitions.

Contribution

It provides the first microscopic imaging evidence of homogeneous superfluid density and pinned vortices in UTe$_2$, supporting a specific superconducting order parameter.

Findings

Homogeneous superfluid density observed near the surface.

Temperature dependence consistent with an anisotropic gap.

No evidence of multiple phase transitions in superfluid density.

Abstract

The spin-triplet superconductor UTe$_2$ shows spontaneous time-reversal symmetry breaking and multiple superconducting phases in some crystals, implying chiral superconductivity. Here we microscopically image the local magnetic fields and magnetic susceptibility near the surface of UTe$_2$, observing a homogeneous superfluid density $n_s$ and homogeneous pinned vortices. The temperature dependence of $n_s$ is consistent with an anisotropic gap and shows no evidence for an additional kink that would be expected at any second phase transition. Our findings are consistent with a dominant $B_{3u}$ superconducting order parameter in the case of a quasi-2D Fermi surface and provide no evidence for multiple phase transitions in $n_s(T)$ in UTe$_2$.