We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar being 0.3 eV below the Fermi level E_F and a circular Fermi contour around Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic phase which exhibits a topological surface state. The topologically trivial cubic KH stacking shows a valence band maximum at Gamma in line with all previous calculations of the hexagonal stable phase exhibiting the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0 and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around E_F.
@article{arxiv.1308.5859,
title = {Evidence for topological band inversion of the phase change material Ge2Sb2Te5},
author = {Christian Pauly and Marcus Liebmann and Alessandro Giussani and Jens Kellner and Sven Just and Jaime Sánchez-Barriga and Emile Rienks and Oliver Rader and Raffaella Calarco and Gustav Bihlmayer and Markus Morgenstern},
journal= {arXiv preprint arXiv:1308.5859},
year = {2014}
}