Electron-phonon correlations on spin texture of gapped helical Dirac Fermions

TL;DR

This paper investigates how electron-phonon interactions influence the spin texture and spectral properties of gapped helical Dirac fermions on topological insulator surfaces, revealing measurable phonon effects and spin modifications.

Contribution

It introduces a detailed analysis of electron-phonon correlations affecting spin textures and spectral functions in gapped Dirac surface states, highlighting new phonon-induced features.

Findings

Out-of-plane spin component decreases below Fermi momentum

In-plane spin component increases due to electron-phonon interactions

Optical conductivity shows distinct phonon-related structures

Abstract

The metallic surface states of a topological insulator support helical Dirac fermions protected by topology with their spin locked perpendicular to their momentum. They can acquire mass through magnetic doping or through hybridization of states on opposite faces of a thin sample. In this case there can be a component of electron spin oriented perpendicular to the surface plane. The electron-phonon interaction renormalizes the dynamics of the charge carriers through their spectral density. It also modifies the gap channel and a second spectral function enters which, not only determines the out of plane spin component, but also comes into in-plane properties. While the out of plane spin component is decreased below the Fermi momentum ($k_F$), the in plane component increases. There are also correlation tails extending well beyond $k_F$. The angular resolved photo-emission line shapes aquire Holstein side bands. The effective gap in the density of states is reduced and the optical conductivity aquires distinct measurable phonon structure even for modest value of the electron-phonon coupling.