Chiral orbital-angular-momentum in the surface states of Bi2Se3

TL;DR

This study reveals that the orbital angular momentum in Bi2Se3 surface states is significant, chiral, and locked to electron momentum, suggesting new avenues for light-induced spin-polarized currents in topological insulators.

Contribution

The paper demonstrates, through experiments and calculations, that orbital angular momentum in Bi2Se3 surface states is substantial and exhibits chiral locking, a novel insight beyond spin-focused models.

Findings

OAM in Bi2Se3 surface states is significant

OAM is locked to electron momentum in a chiral manner

Potential for strong light-induced spin-polarized currents

Abstract

Locking of the spin of a quasi-particle to its momentum in split bands of on the surfaces of metals and topological insulators (TIs) is understood in terms of Rashba effect where a free electron in the surface states feels an effective magnetic field. On the other hand, the orbital part of the angular momentum (OAM) is usually neglected. We performed angle resolved photoemission experiments with circularly polarized lights and first principles density functional calculation with spin-orbit coupling on a TI, Bi2Se3, to study the local OAM of the surface states. We show from the results that OAM in the surface states of Bi2Se3 is significant and locked to the electron momentum in opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility to have strong light-induced spin-polarized current in the surface states.