Photoinduced pure spin current injection in graphene with Rashba spin-orbit interaction

TL;DR

This paper presents a novel optical method to generate pure spin currents in graphene with Rashba spin-orbit coupling using linearly polarized light, avoiding magnetic fields and ferromagnetic contacts.

Contribution

It introduces a new photoexcitation scheme for spin current injection in graphene that is tunable, efficient, and does not require magnetic fields or ferromagnetic contacts.

Findings

Spin current polarization up to 75% predicted.

Spin current injection is tunable via bias voltage.

Method works over a wide frequency range.

Abstract

We propose a photoexcitation scheme for pure spin current generation in graphene subject to a Rashba spinorbit coupling. Although excitation using circularly-polarized light does not result in optical orientation of spins in graphene unless an additional magnetic field is present, we show that excitation with linearly-polarized light at normal incidence yields spin current injection without magnetic field. Spins are polarized within the graphene plane and are displaced in opposite directions, with no net charge displacement. The direction of the spin current is determined by the linear polarization axis of the light, and the injection rate is proportional to the intensity. The technique is tunable via an applied bias voltage and is accessible over a wide frequency range. We predict a spin current polarization as high as 75% for photon frequencies comparable to the Rashba frequency. Spin current injection via optical methods removes the need for ferromagnetic contacts, which have been identified as a possible source of spin scattering in electrical spin injection in graphene.