Direct mapping of the spin-filtered surface bands of a three-dimensional quantum spin Hall insulator

TL;DR

This study used spin-resolved photoemission spectroscopy to directly map the spin-filtered surface bands of a 3D quantum spin Hall insulator, confirming its topological nature and theoretical predictions.

Contribution

It provides the first direct experimental mapping of spin-filtered surface bands in a 3D quantum spin Hall insulator, validating theoretical models.

Findings

Identification of a spin-up band crossing the Fermi level

Confirmation of the strong topological insulator phase

Determination of mirror chirality as -1

Abstract

Spin-polarized band structure of the three-dimensional quantum spin Hall insulator $\rm Bi_{1-x}Sb_{x}$ (x=0.12-0.13) was fully elucidated by spin-polarized angle-resolved photoemission spectroscopy using a high-yield spin polarimeter equipped with a high-resolution electron spectrometer. Between the two time-reversal-invariant points, $\bar{\varGamma}$ and $\bar{M}$, of the (111) surface Brillouin zone, a spin-up band ($\Sigma_3$ band) was found to cross the Fermi energy only once, providing unambiguous evidence for the strong topological insulator phase. The observed spin-polarized band dispersions determine the "mirror chirality" to be -1, which agrees with the theoretical prediction based on first-principles calculations.