Anisotropic effect of warping on the lifetime broadening of topological surface states in angle-resolved photoemission from Bi$_2$Te$_3$

TL;DR

This paper investigates how hexagonal warping in Bi$_2$Te$_3$ affects the anisotropic lifetime broadening of topological surface states, revealing spin-dependent scattering processes that influence surface scattering.

Contribution

It demonstrates the anisotropic lifetime broadening caused by warping and proposes spin-dependent scattering as the underlying mechanism, advancing understanding of topological insulator surface states.

Findings

Anisotropic lifetime broadening observed along different crystallographic directions.

Warping causes deviation from linear Dirac cone dispersion.

Spin-dependent scattering processes explain anisotropic scattering rates.

Abstract

We analyze the strong hexagonal warping of the Dirac cone of Bi$_2$Te$_3$ by angle-resolved photoemission. Along $\overline{\Gamma}$$\overline{\rm M}$, the dispersion deviates from a linear behavior meaning that the Dirac cone is warped outwards and not inwards. We show that this introduces an anisotropy in the lifetime broadening of the topological surface state which is larger along $\overline{\Gamma}$$\overline{\rm K}$. The result is not consistent with nesting. Based on the theoretically predicted behavior of the ground-state spin texture of a strongly warped Dirac cone, we propose spin-dependent scattering processes as explanation for the anisotropic scattering rates. These results could help paving the way for optimizing future spintronic devices using topological insulators and controlling surface-scattering processes via external gate voltages.