Emergence of Triplet Correlations in Superconductor/Half Metallic Nanojunctions with Spin Active Interfaces

Abstract

We study triplet pairing correlations induced in an SFS trilayer (where F is a ferromagnet and S an ordinary s-wave superconductor) by spin flip scattering at the interfaces. We derive and solve self consistently the appropriate Bogoliubov-de Gennes equations in the clean limit. We find that the spin flip scattering generates $m=\pm 1$ triplet correlations, odd in time. We study the general spatial behavior of these and of $m=0$ correlations as a function of position and of spin-flip strength, $H_{spin}$. We concentrate on the case where the ferromagnet is half-metallic. We find that for certain values of $H_{spin}$, the triplet correlations pervade the magnetic layer and can penetrate deeply into the superconductor. The behavior we find depends very strongly on whether the singlet order parameter is in the 0 or $\pi$ state, which must in turn be determined self-consistently. We also present results for the density of states (DOS) and for the local magnetization, which, due to spin-flip processes, is not in general aligned with the magnetization of the half metal, and near the interfaces, rotates as a function of position and $H_{spin}$. The average DOS in both F and S is shown to exhibit various subgap bound states positioned at energies that depend strongly on the particular junction state and the spin