# Field-reentrant superconductivity close to a metamagnetic transition in the heavy-fermion superconductor UTe$_2$

## TL;DR

This study investigates the behavior of superconductivity in UTe$_2$ under high magnetic fields, revealing reentrant superconductivity near a metamagnetic transition and its dependence on magnetic fluctuations and Fermi surface changes.

## Contribution

It provides the first detailed analysis of the upper critical field in UTe$_2$ near a metamagnetic transition, highlighting the interplay between magnetic fluctuations and superconductivity.

## Key findings

- Superconductivity persists up to the metamagnetic transition at ~35 T.
- Superconductivity is suppressed above the metamagnetic transition.
- Reentrant superconductivity occurs at higher temperatures under magnetic fields.

## Abstract

We present a study of the upper critical field of the newly discovered heavy fermion superconductor UTe$_2$ by magnetoresistivity measurements in pulsed magnetic fields up to 60~T and static magnetic fields up to 35~T. We show that superconductivity survives up to the metamagnetic transition at $H_{\rm m} \approx 35$~T at low temperature. Above $H_{\rm m}$ superconductivity is suppressed. At higher temperature superconductivity is enhanced under magnetic field leading to reentrance of superconductivity or an almost temperature independent increase of $H_{\rm c2}$. By studying the angular dependence of the upper critical field close to the $b$ axis (hard magnetization axis) we show that the maximum of the reentrant superconductivity temperature is depinned from the metamagnetic field. A key ingredient for the field-reinforcement of superconductivity on approaching $H_{\rm m}$ appears to be an immediate interplay with magnetic fluctuations and a possible Fermi-surface reconstruction.