Half-Metallic Superconducting Triplet Spin Valve
Klaus Halterman and Mohammad Alidoust
Phys. Rev. B 94, 064503 (2016). [PDF]
We theoretically study a finite size SF1NF2 spin valve, where a normal metal (N) insert separates a thin standard ferromagnet (F1) and a thick half-metallic ferromagnet (F2). For sufficiently thin superconductor (S) widths close to the coherence length ΞΎ0, we find that changes to the relative magnetization orientations in the ferromagnets can result in substantial variations in the transition temperature Tc, consistent with experiment [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Our results demonstrate that, in good agreement with the experiment, the variations are largest in the case where F2 is in a half-metallic phase and thus supports only one spin direction. To pinpoint the origins of this strong spin-valve effect, both the equal-spin f1 and opposite-spin f0 triplet correlations are calculated using a self-consistent microscopic technique. We find that when the magnetization in F1 is tilted slightly out-of-plane, the f1 component can be the dominant triplet component in the superconductor. The coupling between the two ferromagnets is discussed in terms of the underlying spin currents present in the system. We go further and show that the zero energy peaks of the local density of states probed on the S side of the valve can be another signature of the presence of superconducting triplet correlations. Our findings reveal that for sufficiently thin S layers, the zero energy peak at the S side can be larger than its counterpart in the F2 side.
