Enhancement and Discontinuity of Effective Mass through the First-Order Metamagnetic Transition in UTe$_2$

TL;DR

This study investigates the metamagnetic transition in UTe$_2$, revealing how effective mass changes discontinuously at the transition and influences reentrant superconductivity, using combined magnetization and temperature measurements.

Contribution

It provides the first detailed analysis of effective mass enhancement and discontinuity across the metamagnetic transition in UTe$_2$ using combined thermodynamic measurements.

Findings

Effective mass significantly enhances near the metamagnetic transition.

Discontinuous decrease of effective mass for H||b above Hm.

Discontinuous increase of effective mass for H||[011] above Hm.

Abstract

Metamagnetic transitions in the novel spin-triplet superconductor UTe$_2$ were investigated through the newly developed simultaneous measurements of magnetization and sample temperature for the field along the orthorhombic $b$-axis and close to the [011] direction, where reentrant superconductivity (RSC) is detected below and above the first-order metamagnetic transition field $H_{\rm m}$. Combining the Maxwell's relation and the Clausius-Clapeyron equation, we obtained the field dependence of Sommerfeld coefficient $\gamma$ through the first-order metamagnetic transition. A significant enhancement of the effective mass toward $H_{\rm m}$ were detected for both field directions. On the other hand, above $H_{\rm m}$, the effective mass discontinuously decreases for $H~||~b$, while it discontinuously increases for $H~||~\sim [011]$, which seems to make a crucial role for the RSC.