Magnetic-Field-Induced Phenomena in the Paramagnetic Superconductor UTe₂

We present magnetoresistivity measurements on the heavy-fermion superconductor UTe₂ in pulsed magnetic fields µ₀H up to 68 T and temperatures T from 1.4 to 80 K. Magnetic fields applied along the three crystallographic directions a (easy magnetic axis), b, and c (hard magnetic axes), are found to induce different phenomena - depending on the field direction - beyond the low-field suppression of the superconducting state. For H k a, a broad anomaly in the resistivity is observed at µ₀H^∗ ' 10 T and T = 1.4 K. For H k c, no magnetic transition nor crossover are observed. For H k b, a sharp first-order-like step in the resistivity indicates a metamagnetic transition at the field µ₀H_m ' 35 T. When the temperature is raised signature of first-order metamagnetism is observed up to a critical endpoint at T_CEP ' 7 K. At higher temperatures a crossover persists up to 28 K, i.e., below the temperature T_χ^max = 35 K where the magnetic susceptibility is maximal. A sharp maximum in the Fermi-liquid quadratic coefficient Aof the low-temperature resistivity is found at H_m. It indicates an enhanced effective mass associated with critical magnetic fluctuations, possibly coupled with a Fermi surface instability. Similarly to the URhGe case, we show that UTe₂ is a candidate for field-induced reentrant superconductivity in the proximity of H_m.