Ab initio calculation of transverse spin current in graphene nanostructures

We report a theoretical analysis of transverse spin current in a four-probe graphene nanostructure in the absence of spin-orbit interaction and magnetic field. The nanostructure consists of a finite-size graphene sheet connected to the outside world by two zigzag graphene nanoribbons (GNR) and two armchair graphene nanoribbons, forming a cross-shaped two-dimensional device. Due to edge state induced magnetism at zigzag GNR boundaries, our result shows that a pure transverse spin current without an accompanying charge current is induced. We have calculated the transverse spin conductance by an atomic first-principles method where density-functional theory is carried out within the Keldysh nonequilibrium Green's function framework.