Dresden 2017 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 46: Electronic Structure of Surfaces: Spectroscopy, Surface States

O 46.7: Poster

Dienstag, 21. März 2017, 18:30–20:30, P1A

Investigation of charge puddles at the surface of the compensated topological insulator BiSbTeSe2 — •Timo Knispel, Wouter Jolie, Nick Borgwardt, Zhiwei Wang, Jonathan Lux, Achim Rosch, Yoichi Ando, Markus Grüninger, and Thomas Michely — II. Physikalisches Institut, Universität zu Köln, Germany

BiSbTeSe2 is a three dimensional topological insulator which is characterized by an insulating bulk state and a gapless Dirac cone at the Γ-point, with the chemical potential near the Dirac point [1]. Large fluctuations in the Coulomb potential of the dopants cause self-organized charge puddles in the bulk, which in turn cause substantial rigid shifts of the local bulk band structure. Surprisingly, these charge puddles evaporate around 50 K [2]. Here we investigate by STM and STS charge puddles at the surface of BiSbTeSe2 and how they are linked to the bulk ones.

In atomic resolution STM and STS measured over a broad energy range we identify (i) a short length scale due to variations in chemical composition, (ii) a medium energy-dependent length scale due to quasiparticle scattering, and (iii) a large length scale which we attribute to surface charge puddles. By point spectroscopy we measure Dirac point fluctuations of Δ E=25 meV around an average of +30 meV. Through temperature dependent experiments we analyze the coupling of the surface charge puddles to their bulk counterparts.

[1] T. Arkane et al., Nat. Comm. 3, 636 (2012)

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

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