The co-existence of superconductivity and ferromagnetism in actinide compounds

Recently superconductivity has been observed in two different 5f-electron ferromagnets, UGe2 and URhGe, well below their Curie temperatures. While superconductivity could be generic to all clean ferromagnets an alternative possibility is that it occurs in these materials, which were after all carefully selected for study, due to some special features related to the participation of strongly correlated 5f electrons in the ferromagnetism. 5f electrons potentially give rise to strong anisotropies, strong spin-orbit interactions and also a strong energy dependence of the electronic density of states. Here we focus on UGe2, and review several of the properties of the ferromagnetic state that could be a consequence of such features and discuss whether they promote superconductivity.