Reinforcement of superconductivity by quantum critical fluctuations of metamagnetism in UTe2

The normal -conducting state of the superconductor UTe2 is studied by entropy analysis for magnetic fields along the b axis, obtained from magnetization using the relation ( 8 M /8 T )( B )= ( 8 S /8 B )( T) . We observe a strong increase in entropy with magnetic field due to metamagnetic (MM) fluctuations (spatially uniform, Q = 0). The field dependence is well described by the Hertz-Millis-Moriya theory for quantum criticality of itinerant MM. Notably, the lower bound of the quantum -critical region coincides well with the position of the minimum in the superconducting transition temperature T-c ( B ). Hence, our results suggest that Q = 0 fluctuations reinforce the superconductivity.