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TT: Fachverband Tiefe Temperaturen
TT 28: Poster Session: Topological Topics
TT 28.7: Poster
Monday, March 12, 2018, 15:00–19:00, Poster B
Length scale of puddle formation in 3D topological insulators — Thomas Bömerich, Jonathan Lux, •Qingyufei Terenz Feng, and Achim Rosch — Institut für Theoretische Physik, Univeristät zu Köln, Germany
In most semiconductors and insulators the presence of a small density of charged impurities cannot be avoided, but their effect can be reduced by compensation doping, i.e. by introducing defects of opposite charge. Screening in such a system leads to the formation of electron-hole puddles, which dominate bulk transport, as first recognized by Efros and Shklovskii. Metallic surface states of topological insulators (TI) contribute extra screening channels, suppressing puddles. We investigate the typical length lp, which determines the distance between puddles and the suppression of puddle formation close to metallic surfaces in the limit where the gap Δ is much larger than the typical Coulomb energy Ec of neighboring dopants, Δ≫ Ec. In particular, this is relevant for three dimensional Bi-based topological insulators, where Δ /Ec∼100. Scaling arguments predict lp∼ (Δ/Ec)2. In contrast, we find numerically that lp is much smaller and grows in an extended crossover regime approximately linearly with Δ/Ec for numerically accessible values, Δ/Ec∼ 35. We show how a quantitative scaling argument can be used to extrapolate to larger Δ/Ec, where lp∼ (Δ/Ec)2/ ln(Δ/Ec). Our results can be used to predict a characteristic thickness of TI thin films, below which the sample quality is strongly enhanced.