Coexistence of superconductivity and ferromagnetism in URhGe

The discovery(1) of superconductivity at high pressure (albeit over a restr icted range) in the ferromagnetic material UGe2 raised the possibility that bulk superconductivity might be found in other ferromagnets. The exact sym metry of the paired state and the dominant mechanism responsible for the pa iring, however, remain unidentified. Meanwhile, the conjecture that superco nductivity could occur more generally in ferromagnets has been fuelled by t he recent observation of a low-temperature transition that suggests an onse t of superconductivity in high-quality crystals of the itinerant-ferromagne t ZrZn2 (ref. 2), although the thermodynamic signature of this transition c ould not be detected. Here we show that the ferromagnet URhGe is supercondu cting at ambient pressure. In this case, we rnd the thermodynamic signature of the transition-its form is consistent with a superconducting pairing of a spin-triplet type, although further testing with cleaner samples is need ed to confirm this. The combination of superconductivity and ferromagnetism may thus be more common and consequently more important than hitherto real ized.