Chiral tunneling in single-layer graphene with Rashba spin-orbit coupling: Spin currents

We study forward scattering of two-dimensional massless Dirac electrons at Fermi energy >0 in single-layer graphene (SLG) through a one-dimensional rectangular barrier of height u0 in the presence of uniform Rashba spin-orbit coupling (of strength λ). The role of the Klein paradox in graphene spintronics is thereby exposed. It is shown that (1) for -2λ<u0< +2λ, there is partial Klein tunneling, the transmission coefficient T(λ)<1, and quite remarkably, T(λ≥0.1meV)≈0 when the scattering energy equals the barrier height =u0 [whereas T(λ=0)=2]. (2) Spin density and spin-current density are remarkably different than in bulk SLG. They are sensitive to λ and u0. (3) Spin current densities are space dependent, implying the occurrence of nonzero spin torque density. Such a system may serve as a graphene-based spintronic device without the use of an external magnetic field or magnetic materials.