Field-angle evolution of the superconducting and magnetic phases of UTe$_2$ around the $b$ axis

TL;DR

This study maps the magnetic-field-induced superconducting and magnetic phases of UTe$_2$ near the $b$ axis, revealing symmetry-consistent phase boundaries, anisotropic critical fields, and unusual normal-state features through high-field magnetoresistance measurements.

Contribution

It provides a detailed three-dimensional phase boundary mapping of UTe$_2$ around the $b$ axis, highlighting symmetry properties and anisotropic behaviors of superconducting and magnetic phases.

Findings

Phase boundaries obey crystallographic symmetries.

Upper critical field fits anisotropic mass model.

Nearly constant boundaries of the $b$-axis superconducting phase up to the metamagnetic transition.

Abstract

We experimentally determine the bounds of the magnetic-field-induced superconducting and magnetic phases near the crystalline $b$ axis of uranium ditelluride (UTe$_2$). By measuring the magnetoresistance as a function of rotation angle and field strength in magnetic fields as large as 41.5 T, we have studied these boundaries in three dimensions of magnetic field direction. The phase boundaries in all cases obey crystallographic symmetries and no additional symmetries, evidence against any symmetry-breaking quadrupolar or higher magnetic order. We find that the upper critical field of the zero-field superconducting state is well-described by an anisotropic mass model. In contrast, the angular boundaries of the $b$-axis-oriented field-reentrant superconducting phase are nearly constant as a function of field up to the metamagnetic transition, with anisotropy between the $ab$ and $bc$ planes that is comparable to the angular anisotropy of the metamagnetic transition itself. We discuss the relationship between the observed superconducting boundaries and the underlying $\mathbf{d}$ vector that represents the spin-triplet order parameter. Additionally, we report an unexplained normal-state feature in resistance and track its evolution as a function of field strength and angle.