Spin and charge transport induced by a twisted light beam on a surface of a topological insulator

TL;DR

This paper theoretically investigates how twisted light beams induce complex spin and charge transport phenomena, including spin vortices and nonlocal currents, on the surface of doped topological insulators due to spin-momentum locking.

Contribution

It reveals the formation of spin vortices and nonlocal charge and spin currents induced by twisted light on TI surfaces, highlighting the role of spin-momentum locking and inhomogeneous electric fields.

Findings

Spin vortices depend on light's angular momentum.

Inhomogeneous electric fields generate nonlocal currents.

Spin-momentum locking is key to unconventional spin structures.

Abstract

We theoretically study spin and charge transport induced by a twisted light beam irradiated on a disordered surface of a doped three dimensional topological insulator (TI). We find that various types of spin vortices are imprinted on the surface of the TI depending on the spin and orbital angular momentum of the incident light. The key mechanism for the appearance of the unconventional spin structure is the spin-momentum locking in the surface state of the TI. Besides, the diffusive transport of electrons under an inhomogeneous electric field causes a gradient of the charge density, which then induces nonlocal charge current and spin density as well as the spin current. We discuss the relation between these quantities within the linear response to the applied electric field using the Keldysh-Green's function method.