Perfect modulation between fully spin-polarized spin-singlet and -triplet Andreev entanglements in a narrow quantum spin Hall system

Abstract

We consider a quantum spin Hall (QSH) insulator strip touching on one s-wave superconductor sandwiched between two ferromagnetic insulators and study its scattering processes, tunneling conductance, and noise power by using an extended Bogoliubov-de Gennes scattering formalism. It is demonstrated that interedge coupling and noncollinear magnetizations allow for producing the usual and novel crossed Andreev reflections (ARs), respectively, and thus the corresponding spin-singlet and -triplet pairing entanglements. Moreover, by proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, not only perfect but also fully spin-polarized crossed AR at any magnetic orientational angle α is exhibited, which can be experimentally confirmed by the tunneling conductance and noise power. Particularly, the perfect and fully spin-polarized modulation between the spin-singlet and -triplet Andreev entanglements could be performed by α at certain energy values, which suggest that the setup can act as a topological superconducting spintronic device with such a manipulation function.