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

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 H-m approximate to 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 H-c2. 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.