Sudden adiabaticity entering field-induced state in UTe2

TL;DR

This study provides definitive thermodynamic evidence for a bulk field-induced superconducting state in UTe2 at high magnetic fields, using thermal, electrical, and magnetic probes up to 55 T.

Contribution

It demonstrates the first clear thermodynamic and thermal evidence for a bulk field-induced superconducting phase in UTe2 at high magnetic fields.

Findings

Detection of low or vanishing electrical resistance in high fields.

Magnetocaloric measurements show adiabatic behavior consistent with superconductivity.

Evidence supports the existence of a bulk field-induced superconducting state.

Abstract

There has been a recent surge of interest in UTe$_2$ due to its unconventional magnetic field (H) reinforced spin-triplet superconducting phases persisting at fields far above the simple Pauli limit for H $\parallel$ [010]. Magnetic fields in excess of 35 T then induce a field-polarized magnetic state via a first-order-like phase transition. More controversially, for field orientations close to H $\parallel$ [011] and above 40 T, electrical resistivity measurements suggest that a further superconducting state may exist. However, no Meissner effect or thermodynamic evidence exists to date for this phase making it difficult to exclude a simple low-resistance metallic state. In this paper, we describe a study using thermal, electrical, and magnetic probes in magnetic fields of up to 55 T applied between the [010] ($b$) and [001] ($c$) directions. Our MHz conductivity data reveal the field-induced state of low or vanishing electrical resistance; simultaneous magnetocaloric effect measurements (i.e. changes in sample temperature due to changing magnetic field), show the first definitive evidence for adiabaticity and thermal behavior characteristic of bulk field-induced superconductivity.