# Metamagnetic Transition in Heavy Fermion Superconductor UTe2

## TL;DR

This study reveals a first-order metamagnetic transition in UTe2 at 34.9 T, with associated effective mass enhancement, providing insights into its field-robust superconductivity and related heavy fermion behavior.

## Contribution

The paper reports the observation of a metamagnetic transition and effective mass enhancement in UTe2, advancing understanding of its magnetic and superconducting properties under high magnetic fields.

## Key findings

- Metamagnetic transition at 34.9 T along the b-axis.
- Critical end point at ~11 K and 34.8 T.
- Significant effective mass enhancement at the transition.

## Abstract

We have studied the magnetization of the recently discovered heavy fermion superconductor UTe$_2$ up to 56 T in pulsed-magnetic fields. A first-order metamagnetic transition has been clearly observed at $H_{\rm m}$ =34.9 T when the magnetic field $H$ is applied along the orthorhombic hard-magnetization $b$-axis. The transition has a critical end point at $\sim$11 K and 34.8 T, where the first order transition terminates and changes into a crossover regime. Using the thermodynamic Maxwell relation, we have evaluated the field dependence of the Sommerfeld coefficient of the specific heat directly related to the superconducting pairing. From the analysis, we found a significant enhancement of the effective mass centered at $H_{\rm m}$, which is reminiscent of the field-reentrant superconductivity of the ferromagnet URhGe in transverse fields. We discuss the origin of their field-robust superconductivity.