Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment

TL;DR

This study combines experimental photoelectron spectroscopy and advanced ab-initio calculations to demonstrate that Bi2Se3, a topological insulator, possesses a direct band gap at the Gamma point, clarifying its electronic structure.

Contribution

The paper provides the first combined experimental and theoretical evidence confirming the direct band gap at the Gamma point in Bi2Se3, emphasizing the importance of many-body effects in theoretical models.

Findings

Bi2Se3 has a direct band gap at the Gamma point.

Many-body effects are crucial for accurate band structure predictions.

Experimental band mapping confirms theoretical predictions.

Abstract

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Gamma point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Brillouin center only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center.