Electrical control of equal-spin Andreev reflection and magnetoresistance in silicene-based noncollinear ferromagnetic superconducting heterojunctions

The equal- and opposite-spin pairing correlations in silicene-based ferromagnet/ferromagnet/superconductor (F/F/SC) and F/F/SC/F/F junctions controlled by electric field are investigated. The noncollinear magnetization is a necessary condition for generating the novel Andreev reflection (NAR), novel crossed Andreev reflection (NCAR), and spin-flip elastic cotunneling (SFEC) processes, due to the spin-flip scattering at the F/F interface. Different from conventional scattering, the strong signal of spin-flip scattering process is distributed in finite polar and azimuthal angle spaces. A switch effect between conventional AR (CAR) and NAR (NCAR) can be realized in the F/F/SC (F/F/SC/F/F) junction by tuning the exchange and electric fields. The EC conductance is symmetric about the azimuthal angle $\ensuremath{\varphi}=\ensuremath{\pi}$, whereas the spin-flip scattering breaks the symmetry leading to an asymmetrical SFEC conductance. Different from spin polarization, the valley polarization for both the conventional AR and NAR can be tuned from 100% to $\ensuremath{-}100$% by reversing the directions of not only exchange field but also electric field. Moreover, the more the exchange energy approaches zero (Fermi energy), the larger the negative maximum value of the nonlocal (local) magnetoresistance becomes.