Perfect switching of the spin polarization in a ferromagnetic gapless graphene/superconducting gapped graphene junction

Abstract

With the fabrication of gapped graphene, interest in the tunneling spectroscopy in graphene-based FG/SG junctions in which one side consists of a gapless ferro-magnetic graphene (FG) and the other side, of a gapped superconducting graphene (SG) has arisen. The carriers in the gapless (gapped) graphene are 2D relativistic particles having an energy spectrum given by E = sqrt(􀔰2 vF 2 k2 +(mvF 2)2) (where mvF 2 is the gap and vF is the Fermi velocity). The spin currents in this FG/SG junction are obtained within the framework of the extended Blonder-Tinkham-Klapwijk (BTK) formalism. The effects of the superconducting energy gap in SG, of the gap mvF 2 which opened in the superconducting graphene, of the exchange field in FG, of the spin-dependent specular Andreev reflection, of the effective Fermi energy (EFF) of FG and of the bias voltage across the junction (V) are simulated. It is seen that by adjusting EFF or V, the spin polarization (defined as SP(%) = 100% × (G↑ - G↓)/(G↑ + G↓)) can be switched from a pure spin up (SP = +100%) state to pure spin down (SP = -100%) state.