Probing two topological surface bands of Sb2Te3 by spin-polarized photoemission spectroscopy

TL;DR

This study uses spin- and angle-resolved photoemission spectroscopy combined with density functional theory to map and analyze the spin texture and electronic structure of Sb2Te3's surface states, revealing a topologically protected Dirac cone and a novel spin-split surface band.

Contribution

It provides the first detailed experimental and theoretical characterization of the spin texture and surface states of Sb2Te3, including a newly observed spin-split surface band protected by symmetry.

Findings

Sb2Te3 exhibits a single spin-Dirac cone around the Fermi energy.

The Dirac cone states have 80-90% spin polarization.

A novel spin-split surface band is observed at 0.8 eV below the Fermi level.

Abstract

Using high resolution spin- and angle-resolved photoemission spectroscopy, we map the electronic structure and spin texture of the surface states of the topological insulator Sb2Te3. In combination with density functional calculations (DFT), we directly show that Sb2Te3 exhibits a partially occupied, single spin-Dirac cone around the Fermi energy, which is topologically protected. DFT obtains a spin polarization of the occupied Dirac cone states of 80-90%, which is in reasonable agreement with the experimental data after careful background subtraction. Furthermore, we observe a strongly spin-orbit split surface band at lower energy. This state is found at 0.8eV below the Fermi level at the gamma-point, disperses upwards, and disappears at about 0.4eV below the Fermi level into two different bulk bands. Along the gamma-K direction, the band is located within a spin-orbit gap. According to an argument given by Pendry and Gurman in 1975, such a gap must contain a surface state, if it is located away from the high symmetry points of the Brillouin zone. Thus, the novel spin-split state is protected by symmetry, too.