Retro and specular Andreev reflections and valley-spin switching effect in graphene superconducting heterojunction

Abstract

We investigated Andreev reflection of graphene-based normal/superconductor single and double junctions under the modulation of non-resonant circularly polarized light, staggered potential, and exchange field. In the graphene-based normal/superconductor single junction, we discovered that the circularly polarized light can adjust the bandgap of retro Andreev reflection and specular Andreev reflection. The exchange field can change the position of the transition point between retro Andreev reflection and specular Andreev reflection. In the graphene-based normal/superconductor/normal double junction, when the light field is modulated from left circularly polarized light to right circularly polarized light, the valley-spin switching effect between pure elastic co-tunneling and pure crossed Andreev reflection can be realized. By changing the exchange field, we achieved the conversion of non-local transport between pure elastic co-tunneling and pure crossed Andreev reflection. In addition, the energy location and range of crossed Andreev reflection and elastic co-tunneling can be controlled by the staggered potential and the exchange field. Our results suggest that the device can implement light and exchange field control of the Andreev reflection process and the spin-valley switch.