Dai Aoki (Tohoku University) “Multiple Superconducting Phases and Field-induced Phenomena in UTe2”

ABSTRACT: We present our recent results on heavy fermion paramagnet UTe2 as a candidate for novel spin-triplet superconductivity. The large specific heat jump at Tc=1.7 indicates a strong coupling superconductor. The huge upper critical field exceeding the Paul limit for all field directions suggests the spin-triplet state. One of the highlights in UTe2 is the field-reentrant superconductivity surviving up to the first-order metamagnetic transition field, 35T. The pressure also induces the exotic superconducting properties, revealing the split of Tc above ~0.3GPa and the multiple superconducting phases up to the critical pressure 1.5GPa. Finally, the magnetic order suppresses the superconducting phases at higher pressure. These unusual superconducting properties seem to be driven by complex fluctuations, such as antiferromagnetic, ferromagnetic, valence, and Fermi surface instabilities, with the unique crystal structure, which is discussed through the comparison to ferromagnetic superconductors, URhGe and UCoGe.