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 mu H-0(m) = 36.0T 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 gamma(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 gamma(N) indicates that quantum fluctuation strongly evolves around H-m; it assists the superconductivity emerging even in extremely high fields.