Reinforcement of superconductivity by quantum critical fluctuations of metamagnetism in UTe

Tokiwa, Yoshifumi  ; Opletal, P.  ; Sakai, Hironori   ; Kambe, Shinsaku  ; Yamamoto, Etsuji  ; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Haga, Yoshinori   ; Tokunaga, Yo  

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