Coexistence of Superconductivity and Ferromagnetism

Abstract

An overview of the problem of the coexistence of superconductivity and ferromagnetism in uranium-based superconductors such as UGe2, URhGe, UCoGe, UIr and ZrZn2 will be briefly presented. Starting with a pairing Hamiltonian with equal spin superconducting triplet pairs and using quantum field theory Green function formalism, the coexistent ferromagnetic order with superconductivity will be shown to be a very distinct possibility. The singlet superconductivity coexisting with ferromagnetism is against the experimental observations. It will be argued that the superconductivity can be destroyed at two points as a result of magnetic fields both intrinsic and or extrinsic, and thus establishing reentrant superconductivity as observed most recently in URhGe. In the absence of consensus on the mechanism, the same is not highlighted although the magnetic quantum fluctuations emanating from quantum critical point could provide the pairing. The limitations of the model will also be discussed.