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  Pauly, Ch.; Liebmann, M.; Giussani, A.; Kellner, J.; Just, S.; Sánchez-Barriga, J.; Rienks, E.; Rader, O.; Calarco, R.; Bihlmayer, G.; Morgenstern, M.: Evidence for topological band inversion of the phase change material Ge₂Sb₂Te₅. Applied Physics Letters 103 (2013), p. 243109/1-4

10.1063/1.4847715
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Abstract:
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 EF and a circular Fermi contour around Gamma bar with a dispersing diameter of 0.27–0.36 A-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 Kooi-De Hosson 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 Z2 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 EF.