Triplet proximity effects in superconductor/ferromagnet hybrid structures exhibiting intrinsic spin–orbit coupling

Abstract

The conventional spin–singlets with momentum zero can be transformed into spin-polarized triplet states with non-zero momentum at the superconductor/ferromagnet interface by an inhomogeneous magnetic exchange field. While the decaying spectrum of triplet pairs in ferromagnetic metals has received significant attention, less is known about the decay of these pairs in ferromagnets with intrinsic spin–orbit coupling (SOC) present at the superconductor/ferromagnet interface. We have performed simulations to study the triplet proximity effects in hybrid structures composed of a BCS superconductor and ferromagnet with intrinsic spin orbit coupling (SOC) in the diffusive limit where the quasiclassical boundary conditions have been modified to incorporate the effect of SO coupling in Usadel equations and the self-consistent equation. We laid emphasis on the modification of the density of states inside the ferromagnet near the Fermi energy. The generated short ranged triplets (SRTs) present themselves in the form of zero energy gap in the density of states (DOS) even in the presence of comparatively larger values of the exchange field oriented either in plane or out of plane of the hybrid structure and the Long ranged triplets (LRTs) present themselves in the form of zero energy peak in the DOS for feasible magnitude and orientation of the exchange field. Understanding and modeling these observations is important as it is difficult to model such hybrid structures experimentally. Where earlier research has focused on the scenario of substantial spin orbit coupling in the ballistic threshold/clean limit, in this paper we provide conclusions that are applicable to the diffusive transport/dirty limit regime. Also, the findings reveal that the SO coupling generates a distinct imprint in the DOS, which exhibits extremely nonmonotonic behavior with magnetization orientations.