Boosted magnetic fluctuations at the onset of superconductivity in UTe$_2$ beyond 40 T

TL;DR

This study reveals enhanced magnetic fluctuations at high magnetic fields in UTe$_2$, correlating with the emergence of superconductivity beyond 40 T, suggesting a magnetic fluctuation-driven mechanism.

Contribution

It provides experimental evidence of boosted quantum-critical magnetic fluctuations associated with high-field superconductivity in UTe$_2$, advancing understanding of magnetic mechanisms in unconventional superconductors.

Findings

Maximum Fermi-liquid coefficient $A$ is enhanced near the metamagnetic transition.

Superconductivity stabilizes beyond the metamagnetic field at high magnetic tilt angles.

Enhanced magnetic fluctuations are linked to the high-field superconducting phase.

Abstract

Several unconventional superconducting phases have been discovered close to a metamagnetic transition in the heavy-fermion compound UTe$_2$. Although suspected to be of magnetic nature, the mechanisms stabilizing these superconducting phases remain mysterious. Here, we present electrical-resistivity measurements on UTe$_2$, with a current $\mathbf{I}\parallel\mathbf{a}$ and under pulsed magnetic fields up to 60~T rotating in the ($\mathbf{b}$,$\mathbf{c}$) plane. We find that the maximum of the Fermi-liquid coefficient $A$ at the metamagnetic transition is enhanced under magnetic fields tilted by $30-40~^\circ$ from $\mathbf{b}$ to $\mathbf{c}$. The enhancement of $A$ coincides with the stabilization of superconductivity in the polarized paramagnetic regime beyond the metamagnetic field $\mu_0H_m\gtrsim40$~T. It is the signature of a boosted quantum-critical magnetic-fluctuation mode probably in play for the mechanism of this superconducting phase. This result appeals for descriptions of the interplay between magnetic-field-induced superconductivity and quantum critical magnetic properties.