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HL: Fachverband Halbleiterphysik
HL 5: Topological insulators
HL 5.2: Vortrag
Montag, 1. April 2019, 09:45–10:00, H36
Nanoscale spectroscopy of surface states on a three-dimensional topological insulator — •Fabian Sandner1, Fabian Mooshammer1, Markus A. Huber1, Martin Zizlsperger1, Helena Weigand1, Markus Plankl1, Christian Weyrich2, Martin Lanius2, Jörn Kampmeier2, Gregor Mussler2, Detlev Grützmacher2, Jessica L. Boland1, Tyler L. Cocker3, and Rupert Huber1 — 1Department of Physics, University of Regensburg, 93040 Regensburg, Germany — 2PGI-9, Forschungszentrum Jülich, 52425 Jülich, Germany — 3Department of Physics and Astronomy, Michigan State University, 48824 Michigan, USA
Massless Dirac fermions in topologically protected surface states (TSSs) make three-dimensional topological insulators (TIs) a promising material class for future high-speed electronics. However, recent reports outline the coexistence of the TSSs and an additional two-dimensional electron gas (2DEG) at TI surfaces due to band bending effects. Here, we use near-field microscopy in the mid-infrared spectral range to probe the local surface properties of (Bi0.5Sb0.5)2Te3 structures with tomographic, three-dimensional precision on the nanoscale. Applying nano-spectroscopy, we retrieve the full complex-valued local dielectric function of the surface states without making a priori model assumptions on the spectral response. In this way, we identify a sharp Lorentzian resonance originating from intersubband transitions of the massive 2DEG, and a broadband absorption background in the dielectric function, which we attribute to transitions between the TSSs and the lowest 2DEG subband.