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.

Direct coupling-induced pseudoparity nonconservation scattering: bipolar spin diode and unipolar spin entanglement pairing

“…A Cooper pair can be spatially deformed by the inverse nonlocal or crossed Andreev reflection (CAR), a process which emits two spin entangled electrons in two conventional metallic leads, where they can be probed separately [7][8][9][10][11]. Therefore, a lot of Cooper pair splitters have been theoretically put forward and experimentally implemented in part, where an SC is coupled with quantum dots [12,13], carbon nanotubes [14,15], Luttinger liquid wires [16], graphenes [17,18], spin quantum Hall insulators [19,20], quantum anomalous Hall insulators [6], etc. However, besides the CAR, there also exists local Andreev reflection (LAR) [21], particularly, the CAR is often completely masked by another nonlocal process known as electron cotunneling (EC) [6,22,23], which does not involve Cooper pairs and is therefore a parasitic process.…”