P-Wave Superconductivity in the Ferromagnetic Superconductor URhGe

Abstract

We report that the upper critical field of single crystals of URhGe exceeds the usual paramagnetic limitation for fields applied along all three crystal axes. In detail the temperature dependence of the critical field cannot be reconciled with opposite-spin pairing but is well described by a single component odd-parity polar order parameter with a maximum gap parallel to the $a$ axis.