Comparison of two superconducting phases induced by a magnetic field in UTe2

TL;DR

This study investigates the complex behavior of superconductivity in UTe2 under different magnetic field orientations, revealing that superconductivity can be reinforced or induced beyond a critical field, with similar normal state properties despite different field directions.

Contribution

It provides a detailed phase diagram of UTe2 under two magnetic field directions, confirming field-induced superconductivity beyond the metamagnetic transition and analyzing the normal state similarities.

Findings

Superconductivity is reinforced near the metamagnetic transition for H || b.

Superconductivity is induced beyond the transition in tilted magnetic fields.

Normal state properties are surprisingly similar for different field directions.

Abstract

Superconductivity induced by a magnetic field near metamagnetism is a striking manifestation of magnetically-mediated superconducting pairing. After being observed in itinerant ferromagnets, this phenomenon was recently reported in the orthorhombic paramagnet UTe$_2$. Under a magnetic field applied along the hard magnetization axis b, superconductivity is reinforced on approaching metamagnetism at $\mu_0H_m$ = 35 T, but it abruptly disappears beyond $H_m$. On the contrary, field-induced superconductivity was reported beyond $\mu_0H_m$ = 40-50 T in a magnetic field tilted by $\simeq25-30\deg$ from b in the (b,c) plane. Here we explore the phase diagram of UTe2 under these two magnetic-field directions. Zero-resistance measurements permit to confirm unambiguously that superconductivity is established beyond Hm in the tilted-field direction. While superconductivity is locked exactly at fields either smaller (for a H || b), or larger (for H tilted by $\simeq27\deg$ from b to c), than Hm, the variations of the Fermi-liquid coefficient in the electrical resistivity and of the residual resistivity are surprisingly similar for the two field directions. The resemblance of the normal states for the two field directions puts constraints for theoretical models of superconductivity and implies that some subtle ingredients must be in play.