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HL: Fachverband Halbleiterphysik

HL 34: Quantum dots and wires: Theory

HL 34.3: Talk

Tuesday, March 12, 2013, 10:00–10:15, H15

Topological phase transitions in α-Sn Nanocrystals: a first-principle approach — •Küfner Sebastian, Jürgen Furthmüller, Martin Fitzner, Lars Matthes, and Friedhelm Bechstedt — Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena

Nanostucturing significantly changes the properties of materials. This especially holds for nanocrystals (NCs). The increased surface to volume ratio influences the electronic structure. There is a strong dependence of the electronic properties on the geometry, the size, and the surface passivation of the nanoscale objects. α-Sn is a zero-gap semiconductor with an inverted band structure at the Γ-point with respect to other group-IV semiconductors. Using density-functional theory within local XC-functionals we show that the level-ordering of s- and p- like states at Γ is inverted in nanocrystals with respect to the bulk. Since the fundamental energy gap decreases for increased nanodot-diameter, we show that there has to be a phase transition for a diameter of about 13 nm where the level odering changes. We determine this critical dot-size by tight-binding calculations. Furthermore, we prove that our results for the fundamental energy gaps of the NCs agree perfectly with methods taking many-body effects and screened Coulomb-interaction into account.