Multiple superconducting phases and field-induced superconductivity under pressure in UTe2

We present our recent results on the novel spin-triplet superconductor UTe2[1,2]. A large jump of the specific heat at 1.6K indicates the strong coupling superconductivity. The huge upper critical field exceeding the Pauli limit indicates the spin-triplet state. For the field along b-axis, the field reentrant superconductivity is observed up to Hm~35T, where the first order metamagnetic transition occurs. The field reentrant superconductivity in UTe2 is similar to that observed in ferromagnetic superconductors, namely URhGe and UCoGe[3,4]. Applying the pressure in UTe2, the superconducting transition temperature splits and the multiple superconducting phases are detected in the AC calorimetry measurements as a thermodynamic response[5,6]. We overview the results on UTe2 comparing with ferromagnetic superconductors, and show our perspective. This work was done in collaboration with G. Knebel, A. Pourret, J.P. Brison, D. Braithwaite, Q. Niu, M. Valiska, J. Flouquet, A. Nakamura, F. Honda, Y. Homma, D.X,Li, Y. Shimizu, Y. J. Sato, A. Miyake, S. Imajo, S. Kohama, M. Tokunaga, H. Harima, W. Knafo, I. Sheikin, C. Paulsen, Y. Tokunaga, S. Kambe, H. Sakai, S. Fujimori, K. Ishida, G. Nakamine, S. Kitagawa.