Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 32: Transport: Topological Insulators - 3D
(Joint session of DS, HL, MA, O and TT organized by TT)
TT 32.2: Vortrag
Dienstag, 8. März 2016, 14:30–14:45, H18
Revealing puddles of electrons and holes in compensated topological insulators — •Nick Borgwardt1, Jonathan Lux2, Zhiwei Wang1,3, Ignacio Vergara1, Malte Langenbach1, Achim Rosch2, Yoichi Ando1,3, Paul van Loosdrecht1, and Markus Grüninger1 — 1II. Physikalisches Institut, Universität zu Köln — 2Institut für theoretische Physik, Universität zu Köln — 3Institute of Scientific and Industrial Research, Osaka University
Three-dimensional topological insulators harbour metallic surface states with exotic properties. In transport or optics, these properties are typically masked by defect-induced bulk carriers. Compensation of donors and acceptors reduces the carrier density, but the bulk resistivity remains disappointingly small. We show that measurements of the optical conductivity in BiSbTeSe2 pinpoint the presence of electron-hole puddles in the bulk at low temperatures, which is essential for understanding DC bulk transport. The puddles arise from large fluctuations of the Coulomb potential of donors and acceptors, even in the case of full compensation. Surprisingly, the number of carriers appearing within puddles drops rapidly with increasing temperature and almost vanishes around 40 K. Monte Carlo simulations show that a highly non-linear screening effect arising from thermally activated carriers destroys the puddles at a temperature scale set by the Coulomb interaction between neighbouring dopants, explaining the experimental observation semi-quantitatively [1].
N. Borgwardt et al., arXiv:1508.03212