Charge and spin supercurrents in triplet superconductor--ferromagnet--singlet superconductor Josephson junctions

TL;DR

This paper investigates the Josephson effect in a triplet superconductor--ferromagnet--singlet superconductor junction, revealing conditions for unconventional charge and spin supercurrents influenced by interface magnetization and phase differences.

Contribution

It introduces a theoretical framework showing how interface magnetization enables unconventional supercurrents in such junctions, confirmed by numerical and analytical methods.

Findings

Charge current depends on magnetization orientation and phase difference.

A phase-dependent spin current exists in the triplet superconductor.

Unconventional Josephson effects are robust beyond tunneling regime.

Abstract

We study the Josephson effect in a triplet superconductor--ferromagnet--singlet superconductor junction. We show that the interaction of tunneling Cooper pairs with the interface magnetization can permit a Josephson current at the lowest order of a tunneling Hamiltonian perturbation theory. Two conditions must be satisfied for this to occur: the magnetization of the ferromagnet has a component parallel to the ${\bf d}$-vector of the triplet superconductor, and the gaps of the superconductors have the same parity with respect to the interface momentum. The resulting charge current displays an unconventional dependence on the orientation of the magnetic moment and the phase difference. This is accompanied by a phase-dependent spin current in the triplet superconductor, while a phase-independent spin current is always present. The tunneling perturbation theory predictions are confirmed using a numerical Green's function method. An analytical treatment of a one-dimensional junction demonstrates that our conclusions are robust far away from the tunneling regime, and reveals signatures of the unconventional Josephson effect in the critical currents.