Field-Reentrant Superconductivity Close to a Metamagnetic Transition in the Heavy-Fermion Superconductor UTe 2

We present a study of the upper critical field of the newly discovered heavy fermion superconductor UTe₂ by magnetoresistivity measurements in pulsed magnetic fields up to 60~T and static magnetic fields up to 35~T. We show that superconductivity survives up to the metamagnetic transition at Hₘ ≈ 35~T at low temperature. Above Hₘ superconductivity is suppressed. At higher temperature superconductivity is enhanced under magnetic field leading to reentrance of superconductivity or an almost temperature independent increase of Hc2. By studying the angular dependence of the upper critical field close to the b axis (hard magnetization axis) we show that the maximum of the reentrant superconductivity temperature is depinned from the metamagnetic field. A key ingredient for the field-reinforcement of superconductivity on approaching Hₘ appears to be an immediate interplay with magnetic fluctuations and a possible Fermi-surface reconstruction.