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

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 $\hat{I}{¼}_0{H}_m\gtrsim 40$~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.

8 pages, 4 Figures + Supplemental Material with 21 pages, 18 Figures