Detecting Chiral Orbital Angular Momentum by Circular Dichroism ARPES

TL;DR

This paper demonstrates that surface electronic bands exhibit a chiral orbital angular momentum structure detectable via circular dichroism ARPES, providing a new way to probe orbital order in materials.

Contribution

It establishes a theoretical framework linking orbital angular momentum in surface bands to circular dichroism ARPES signals, independent of spin-orbit coupling effects.

Findings

Surface bands have a one-to-one correspondence between momentum and orbital angular momentum.

Chiral OAM structure arises from inversion symmetry breaking at surfaces.

Circular dichroism ARPES can effectively detect the orbital angular momentum order.

Abstract

We show, by way of tight-binding and first-principles calculations, that a one-to-one correspondence between electron's crystal momentum k and non-zero orbital angular momentum (OAM) is a generic feature of surface bands. The OAM forms a chiral structure in momentum space much as its spin counterpart in Rashba model does, as a consequence of the inherent inversion symmetry breaking at the surface but not of spin-orbit interaction. Circular dichroism (CD) angle-resolved photoemission (ARPES) experiment is an efficient way to detect this new order, and we derive formulas explicitly relating the CD-ARPES signal to the existence of OAM in the band structure. The cases of degenerate p- and d-orbital bands are considered.