Photoemission Circular Dichroism and Spin Polarization of the Topological Surface States in Ultrathin Bi2Te3 Films

TL;DR

This study investigates the circular dichroism and spin polarization of topological surface states in ultrathin Bi2Te3 films, revealing complex behaviors explained by comprehensive theoretical modeling of photoemission mechanisms.

Contribution

It provides a detailed experimental and theoretical analysis of CD in topological insulator films, clarifying the connection between spin-orbit texture and photoemission signals.

Findings

Complex CD variations with film thickness and photon energy

Sign reversals in CD explained by multiple photoemission mechanisms

Theoretical model accurately describes experimental data

Abstract

Circular dichroism (CD) observed by photoemission, being sensitive to the orbital and spin angular momenta of the electronic states, is a powerful probe of the nontrivial surface states of topological insulators, but the experimental results thus far have eluded a comprehensive description. We report a study of Bi2Te3 films with thicknesses ranging from one quintuple layer (two-dimensional limit) to twelve layers (bulk limit) over a wide range of incident photon energy. The data show complex variations in magnitude and sign reversals, which are nevertheless well described by a theoretical calculation including all three photoemission mechanisms: dipole transition, surface photoemission, and spin-orbit coupling. The results establish the nontrivial connection between the spin-orbit texture and CD.