Anomalous spin Josephson effect in spin superconductors

Abstract

The spin superconductor state is the spin-polarized triplet exciton condensate, which can be viewed as a counterpart of the charge superconductor state. As an analogy of the charge Josephson effect, the spin Josephson effect can be generated in the spin superconductor/normal metal/spin superconductor junctions. Here we study the spin supercurrent in the Josephson junctions consisting of two spin superconductors with noncollinear spin polarizations. For the Josephson junctions with out-of-plane spin polarizations, the possible π-state spin supercurrent appears due to the Fermi momentum-splitting Andreev-like reflections at the normal metal/spin superconductor interfaces. For the Josephson junctions with in-plane spin polarizations, the anomalous spin supercurrent appears and is driven by the misorientation angle of the in-plane polarizations. The symmetry analysis shows that the appearance of the anomalous spin Josephson current is possible when the combined symmetry of the spin rotation and the time reversal is broken.