Theory of spin-polarized superconductors -- an analogue of superfluid ${}^3$He A-phase

Abstract

It is shown theoretically that ferromagnetic superconductors, UGe${}_2$, URhGe, and UCoGe can be described in terms of the A-phase like triplet pairing similar to superfluid ${}^3$He in a unified way, including peculiar reentrant, S-shape, or L-shape $H_{c2}$ curves. The associated double transition inevitable between the A${}_1$ and A${}_2$-phases in the $H$-$T$ plane is predicted, both of which are characterized by non-unitary state with broken time reversal symmetry and the half-gap. UTe${}_2$, which has been discovered quite recently to be a spin-polarized superconductor, is analyzed successively in the same view point, pointing out that the expected A${}_1$-A${}_2$ transition is indeed emerging experimentally. Thus the four heavy Fermion compounds all together are entitled to be topologically rich solid state materials worth further investigating together with superfluid ${}^3$He A-phase.

6 pages, 2 figures