Spin Transport in Graphene Nanoribbons: The Role of Surface-Corrugation

Spin-orbit interaction in flat graphene is rather weak due to the symmetry of the lattice. However, substrate surface-corrugation can break this symmetry and induce a relatively large spin-orbit interaction. In this work we study spin transport in armchair graphene nanoribbons (AGNR) in the presence of substrate surface-corrugation. We employ the non-equilibrium green’s function along with a multiorbital tight-binding model. The role of corrugation amplitude on the spin transmission probability and polarization has been investigated. Due to the low atomic number of carbon, spinorbit coupling in graphene is weak and theoretically a spin relaxation time of about microto millisecond is expected[1]. Experimental studies, however, indicate spin relaxation times in the range of 100− 200ps [2] which are much shorter than the theoretically predicted ones. On the one hand graphene should be placed on a substrate to be used for electronic applications. On the other hand the surface of the substrate is not perfect and can have some degrees of roughness. Surface-corrugation induced curvature can significantly increase spinorbit interaction in graphene [3] which in turn affects spin-relaxation time in this material. The role of surface-corrugation on the electronic charge transport has been studied in Refs. [4], [5]. In this work, for the first time, an atomistic multiorbital Hamiltonian along with the non-equilibrium Green’s function formalism are employed to study the role of surface-corrugation on spin transport in AGNRs. The electronic bandstructure of graphene is described by a nearest neighbor tight-binding model with three orbitals px, py, pz . The hopping parameters are tspσ = +5.580eV, tssσ = −6.769eV, tppσ = +5.037eV, tppπ = −3.033eV [6]. Substrate surface-corrugation modulates bonding lengths and Left-contact Right-contact Spin Flip by Spin-orbit Interaction