Thermodynamic investigation of metamagnetism in pulsed high magnetic fields on heavy fermion superconductor Ute₂

We investigated the thermodynamic property of the heavy fermion superconductor UTe₂ in pulsed high magnetic fields. The superconducting transition in zero field was observed at T_c = 1.65 K as a sharp heat capacity jump. Magnetocaloric effect measurements in pulsed-magnetic fields obviously detected a thermodynamic anomaly accompanied by a first-order metamagnetic transition at μ₀ H_m = 36.0 T when the fields are applied nearly along the hard-magnetization b-axis. From the results of heat capacity measurements in magnetic fields, we found a drastic diverging electronic heat capacity coefficient of the normal state γ_N with approaching H_m. Comparing with the previous works via the magnetic Clausius–Clapeyron relation, we unveil the thermodynamic details of the metamagnetic transition. The enhancement of the effective mass observed as the development of γ_N indicates that quantum fluctuation strongly evolves around H_m; it assists the superconductivity emerging even in extremely high fields.