Anomalous spin Josephson effect in spin superconductors

TL;DR

This paper explores the anomalous spin Josephson effect in spin superconductor junctions, revealing conditions for $ ext{π}$-state and anomalous supercurrents driven by spin polarization orientations and symmetry breaking.

Contribution

It introduces the concept of anomalous spin Josephson effect in spin superconductor junctions with noncollinear spin polarizations, highlighting the role of symmetry breaking.

Findings

π-state spin supercurrent in out-of-plane polarization junctions

Anomalous spin supercurrent driven by in-plane polarization misorientation

Symmetry analysis linking supercurrent to broken combined spin rotation and time reversal symmetry

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 $\pi$-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.