Dresden 2014 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 42: Topological insulators (organized by O)

HL 42.9: Talk

Tuesday, April 1, 2014, 12:30–12:45, GER 38

Evidence for topological band inversion of the phase change material Ge₂Sb₂Te₅ — •Marcus Liebmann¹, Christian Pauly¹, Alessandro Giussani², Jens Kellner¹, Sven Just¹, Jaime Sanchez-Barriga³, Emile Rienks³, Oliver Rader³, Raffaella Calarco², Gustav Bihlmayer⁴, and Markus Morgenstern¹ — ¹II. Inst. Phys. B, RWTH Aachen University — ²Paul-Drude-Institut für Festkörperelektronik, Berlin — ³Helmholtz-Zentrum für Materialien und Energie, BESSY, Berlin — ⁴Peter-Grünberg-Institut and Institute für Advanced Simulation, Forschungszentrum Jülich

We present an angle-resolved photoemission study of the ternary phase change material Ge₂Sb₂Te₅, epitaxially grown on Si(111) in the metastable cubic phase. This material serves, e.g., in DVDs as a fast switchable material (1 ns) between the metallic cubic and an insulating amorphous phase. The observed upper bulk valence band shows a minimum at Γ being 0.3 eV below the Fermi level E_F and a circular Fermi contour around Γ with a dispersing diameter of 0.27−0.36 Å⁻¹. This is in agreement with density functional theory calculations of the Petrov stacking sequence of the cubic phase which is topologically non-trivial. Moreover, the results are in line with all previous calculations of Ge₂Sb₂Te₅ exhibiting the valence band maximum at Γ for a trivial Z₂ topology and away from Γ for a non-trivial one. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around E_F. Our finding opens the perspective of ns-switching between a topological crystalline and an insulating amorphous phase.