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, via the derivation and self-consistent solution of the appropriate Bogoliubov--de Gennes equations in the clean limit. We find that the spin-flip scattering generates $m=\ifmmode\pm\else\textpm\fi{}1$ triplet correlations, odd in time and study the general spatial behavior of these and of $m=0$ correlations as a function of position and of spin-flip strength, ${H}_{spin}$, concentrating on the case where the ferromagnet is half-metallic. 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 $\ensuremath{\pi}$ 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-flip scattering strength.