Magnetic-Field-Induced Phenomena in the Paramagnetic Superconductor UTe₂

Abstract

We present magnetoresistivity measurements on the heavy-fermion\nsuperconductor UTe$_{2}$ in pulsed magnetic fields $\\mu_0H$ up to 68~T and\ntemperatures $T$ from 1.4 to 80~K. Magnetic fields applied along the three\ncrystallographic directions $\\mathbf{a}$ (easy magnetic axis), $\\mathbf{b}$,\nand $\\mathbf{c}$ (hard magnetic axes), are found to induce different phenomena\n- depending on the field direction - beyond the low-field suppression of the\nsuperconducting state. For $\\mathbf{H}\\parallel\\mathbf{a}$, a broad anomaly in\nthe resistivity is observed at $\\mu_0H^*\\simeq10$~T and $T = 1.4$~K. For\n$\\mathbf{H}\\parallel\\mathbf{c}$, no magnetic transition nor crossover are\nobserved. For $\\mathbf{H}\\parallel\\mathbf{b}$, a sharp first-order-like step in\nthe resistivity indicates a metamagnetic transition at the field $\\mu_0H_m\n\\simeq 35$~T. When the temperature is raised signature of first-order\nmetamagnetism is observed up to a critical endpoint at $T_{CEP}\\simeq7$~K. At\nhigher temperatures a crossover persists up to 28~K, i.e., below the\ntemperature $T_\\chi^{max} = 35$~K where the magnetic susceptibility is maximal.\nA sharp maximum in the Fermi-liquid quadratic coefficient $A$ of the\nlow-temperature resistivity is found at $H_m$. It indicates an enhanced\neffective mass associated with critical magnetic fluctuations, possibly coupled\nwith a Fermi surface instability. Similarly to the URhGe case, we show that\nUTe$_{2}$ is a candidate for field-induced reentrant superconductivity in the\nproximity of $H_m$.\n