Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 14: Poster: Two-Dimenaional Materials and Topological Insulators

HL 14.14: Poster

Montag, 20. März 2017, 14:00–18:00, P2-OG3

Puddles in compensated Bi_2−xSb_xTe_3−ySe_y — •Alessandro Revelli¹, Nick Borgwardt¹, Jonathan Lux², Zhiwei Wang¹, Malte Langenbach¹, Achim Rosch², Yoichi Ando¹, Paul van Loosdrecht¹, and Markus Grüninger¹ — ¹II, Physikalisches Institut, Universität zu Köln, Cologne, Germany — ²Institut für theoretische Physik, Universität zu Köln

The topological insulator Bi_2−xSb_xTe_3−ySe_y shows bulk-insulating behaviour due to a low defect density and compensation of acceptors and donors. However, large fluctuations of the Coulomb potential give rise to strong local band bending even in fully compensated samples. This is demonstrated by the formation of electron and hole puddles which some of us have recently detected by infrared absorption measurements on BiSbTeSe₂ [1]. Puddles are important for both bulk and surface properties as they may e.g. yield a spatial variation of the surface charge density. According to Monte Carlo simulations [1], the temperature dependence of puddle formation depends on the Coulomb interaction between defects, while their spectral weight additionally depends on the size of the band gap. To test these predictions and to deepen our understanding of puddles, we performed infrared measurements on Bi_2−xSb_xTe_3−ySe_y as a function of x and y, varying the level of compensation, the defect density, and the band gap. The experimental results are in excellent agreement with the theoretical predictions for puddles in topological insulators.

[1] Borgwardt et al., Phys. Rev. B 93, 245149 (2016).