Spin-conserving and reversing photoemission from the surface states of Bi$_2$Se$_3$ and Au (111)

TL;DR

This paper provides a first-principles theoretical explanation for the tunability of spin polarization in photoemission from Bi$_2$Se$_3$ (111) surface states, contrasting it with the behavior in Au (111), and offers guidance for developing tunable spin-polarized electron sources.

Contribution

It introduces a first-principles theory explaining the band- and wavevector-dependent spin polarization tunability in topological insulator surface states.

Findings

Explains the dependence of spin polarization on band index and wavevector in Bi$_2$Se$_3$.

Shows the absence of tunability in Au (111) surface states.

Provides insights for designing tunable spin-polarized electron sources.

Abstract

We present a theory based on first-principles calculations explaining (i) why the tunability of spin polarizations of photoelectrons from Bi$_2$Se$_3$ (111) depends on the band index and Bloch wavevector of the surface state and (ii) why such tunability is absent in the case of isosymmetric Au (111). The results provide not only an explanation for the recent, puzzling experimental observations but also a guide toward making highly-tunable spin-polarized electron sources from topological insulators.