Reinforcement of superconductivity by quantum critical fluctuations of metamagnetism in UTe2

The normal-conducting state of the superconductor UTe$_2$ is studied by\nentropy analysis for magnetic fields along the $b$-axis, obtained from\nmagnetization using the relation $(\\partial M/\\partial T)_B=(\\partial\nS/\\partial B)_T$. We observe a strong increase in entropy with magnetic field\ndue to metamagnetic fluctuations (spatially uniform, $Q=0$). The field\ndependence is well described by the Hertz-Millis-Moriya theory for quantum\ncriticality of itinerant metamagnetism. Notably, the lower bound of the\nquantum-critical region coincides well with the position of the minimum in the\nsuperconducting transition temperature $T_c(B)$. Hence, our results suggest\nthat $Q=0$ fluctuations reinforce the superconductivity.\n