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We present an angle-resolved photoemission study of a ternary phase changematerial, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastablecubic phase. The observed upper bulk valence band shows a minimum at Gamma-barbeing 0.3 eV below the Fermi level E_F and a circular Fermi contour aroundGamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is inagreement with density functional theory calculations of the Petrov stackingsequence in the cubic phase which exhibits a topological surface state. Thetopologically trivial cubic KH stacking shows a valence band maximum at Gammain line with all previous calculations of the hexagonal stable phase exhibitingthe valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopyexhibits a band gap of 0.4 eV around E_F.

Evidence for topological band inversion of the phase change material Ge2Sb2Te5