Field re-entrant superconductivity induced by the enhancement of effective mass in URhGe

High quality single crystals of a ferromagnetic superconductor URhGe were successfully grown. The electrical resistivity was measured for the field along b-axis in the orthorhombic crystal structure in order to study precisely its field re-entrant superconductivity which occurs in the vicinity of the field H_R, where the easy magnetization switches from c- to b-axis. The field re-entrant superconductivity of URhGe is analyzed with special focus on its dependence with the value of residual resistivity ρ₀ and the coefficient A of T² term of the resistivity. The experimental results are well explained by a crude model related with the field dependence of the effective mass m*, where the corresponding critical temperature T _sc(m*) and the upper critical field H_c2 are strongly enhanced. Discussion is made on the interplay between magnetic and superconducting phase diagram as well as the link between T_sc and A in other heavy fermion superconductors.