Field-Reentrant Superconductivity Close to a Metamagnetic Transition in the Heavy-Fermion Superconductor UTe₂

Abstract

We present a study of the upper critical field of the newly discovered heavy\nfermion superconductor UTe$_2$ by magnetoresistivity measurements in pulsed\nmagnetic fields up to 60~T and static magnetic fields up to 35~T. We show that\nsuperconductivity survives up to the metamagnetic transition at $H_{\\rm m}\n\\approx 35$~T at low temperature. Above $H_{\\rm m}$ superconductivity is\nsuppressed. At higher temperature superconductivity is enhanced under magnetic\nfield leading to reentrance of superconductivity or an almost temperature\nindependent increase of $H_{\\rm c2}$. By studying the angular dependence of the\nupper critical field close to the $b$ axis (hard magnetization axis) we show\nthat the maximum of the reentrant superconductivity temperature is depinned\nfrom the metamagnetic field. A key ingredient for the field-reinforcement of\nsuperconductivity on approaching $H_{\\rm m}$ appears to be an immediate\ninterplay with magnetic fluctuations and a possible Fermi-surface\nreconstruction.\n