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HL: Fachverband Halbleiterphysik

HL 59: Topological insulators: Theory (with MA/O/TT)

HL 59.7: Vortrag

Mittwoch, 2. April 2014, 11:00–11:15, POT 151

Adsorbate- and vacancy-induced band bending in Bi₂Se₃: ab-initio calculations — •Tobias Förster, Peter Krüger, and Michael Rohlfing — Institut für Festkörpertheorie, Westfälische Wilhelms-Universität, 48149 Münster, Germany

Bi₂Se₃ is one of the first topological insulators ever discovered. It has been widely studied both experimentally und theoretically, due to its simple electronic structure with only one Dirac point at Γ. In experiments, a downward band bending and an ageing effect are frequently observed. This has been attributed to an intrinsic n-doping and to coverage with adsorbates. Models for the band bending mostly focussed on the intrinsic doping.

Using DFT calculations, we show that a long-ranged potential also occurs for an adsorbate-covered surface, even without intrinsic doping. As a prototype adsorbate, we have investigated potassium at various coverages. The resulting changes in the charge density, the potential, and the band structure can be attributed to two distinct origins: short-ranged adsorbate-specific changes and the formation of a long-ranged potential (which is independent of the specific adatom). We will explain how the band bending is related to the layered structure of Bi₂Se₃. Similar effects result from our calculations for different types of adsorbates as well as for selenium vacancies in the surface layer.