Observation of warping effects in the band and angular momentum structures of topological insulator Bi2Te3

TL;DR

This study uses ARPES with circularly polarized light to reveal energy-dependent warping effects on orbital angular momentum in Bi2Te3, highlighting deviations from ideal chiral structures near the Fermi level.

Contribution

It demonstrates the strong band warping effects in Bi2Te3 and their impact on the orbital angular momentum structure, supported by experimental ARPES data.

Findings

Strong circular dichroism indicating orbital angular momentum presence

Energy-dependent warping effects alter OAM alignment

Circular dichroism patterns require higher-order sinusoidal terms

Abstract

We performed angle resolved photoemission (ARPES) experiments on Bi2Te3 with circularly polarized light. ARPES data show very strong circular dichroism, indicating existence of orbital angular momentum (OAM). Moreover, the alignment of OAM is found to have a strong binding energy dependence. Such energy dependence comes from a relatively strong band warping effect in Bi2Te3 compared to Bi2Se3. OAM close to Dirac point has an ideal chiral structure (sin ?) without out-of-plane component. Warping effect comes in as the binding energy decreases and circular dichroism along a constant energy contour can no longer be explained by a simple sin? function but requires a sin3? term. When the warping effect becomes even stronger near the Fermi energy, circular dichroism gains an additional sin6? term. Such behavior is found to be compatible with the theoretically predicted OAM structure.