Time-reversal-protected single-Dirac-cone topological-insulator states in Bi2Te3 and Sb2Te3: Topologically Spin-polarized Dirac fermions with pi Berry's Phase

TL;DR

This paper demonstrates that Bi2Te3 and Sb2Te3 are topological insulators with spin-polarized Dirac fermions on their surfaces, characterized by a large bulk band gap and protected by time-reversal symmetry, with potential for topological physics applications.

Contribution

It provides combined theoretical and experimental evidence that Bi2Te3 and Sb2Te3 are Z2 topological insulators with controllable surface Dirac fermions, including effects of Mn doping.

Findings

Bi2Te3 has a ~150 meV bulk band gap with a surface Dirac cone.

Sb2Te3 exhibits similar topological properties despite self-doping.

Surface Dirac fermions are well within the bulk gap and controllable via doping.

Abstract

We show that the strongly spin-orbit coupled materials Bi2Te3 and Sb2Te3 (first non-Bi topological insulator) and their derivatives belong to the Z2 (Time-Reversal-Protected, elastic backscattering suppressed) topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi2Te3 is a large spin-orbit-induced indirect bulk band gap (about 150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb2Te3 exhibits similar Z2 topological properties. We demonstrate that the dynamics of surface spin-only Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for exploring novel topological physics. We emphasize (theoretically and experimentally) that the Dirac node is well within the bulk-gap and not degenerate with the bulk valence band.