Spintronics, or spin electronics, is aimed at efficient control and manipulation of spin degrees of freedom in electron systems. To comply with demands of nowaday spintronics, the studies of electron systems hosting giant spin-orbit-split electron st
ates have become one of the most important directions providing us with a basis for desirable spintronics devices. In construction of such devices, it is also tempting to involve graphene, which has attracted great attention because of its unique and remarkable electronic properties and was recognized as a viable replacement for silicon in electronics. In this case, a challenging goal is to make graphene Dirac states spin-polarized. Here, we report on absolutely new promising pathway to create spin-polarized Dirac states based on coupling of graphene and polar-substrate surface states with giant Rashba-type spin-splitting. We demonstrate how the spin-helical Dirac states are formed in graphene deposited on the surface of BiTeCl. This coupling induces spin separation of the originally spin-degenerate graphene states and results in fully helical in-plane spin polarization of the Dirac electrons.
Within density functional theory, we study bulk band structure and surface states of BiTeBr. We consider both ordered and disordered phases which differ in atomic order in the Te-Br sublattice. On the basis of relativistic ab-initio calculations, we
show that the ordered BiTeBr is energetically preferable as compared with the disordered one. We demonstrate that both Te- and Br-terminated surfaces of the ordered BiTeBr hold surface states with a giant spin-orbit splitting. The Te-terminated surface-state spin splitting has the Rashba-type behavior with the coupling parameter alpha_R ~ 2 eVAA.
