Theory of Spin-polarized Superconductors -An Analogue of Superfluid 3He A-phase

Ferromagnetic superconductors such as UGe2, URhGe, and UCoGe can he described in terms of the A-phase like triplet pairing similar to the superfluid He-3 in a unified manner, including peculiar reentrant, S-shape, or L-shape H-c2 curves. Associated double transition is inevitable between the A(1)- and A(2)-phases in the H-T plane, characterized by their non-unitary state, broken time reversal symmetry, and half-gap. UTe2 discovered recently is analyzed successively in the same manner. We point out that the expected A(1)-A(2) transition is now emerging experimentally. All these compounds are topologically rich solid-state materials worth further investigation.