In situ disentangling surface state transport channels of a topological insulator thin film by gating

• Published in: npj quantum materials 2018-09, Vol.3 (1), Article 46
• Main Authors: Lüpke, Felix, Just, Sven, Eschbach, Markus, Heider, Tristan, Młyńczak, Ewa, Lanius, Martin, Schüffelgen, Peter, Rosenbach, Daniel, von den Driesch, Nils, Cherepanov, Vasily, Mussler, Gregor, Plucinski, Lukasz, Grützmacher, Detlev, Schneider, Claus M., Tautz, F. Stefan, Voigtländer, Bert
• Format: Article
• Language: English
• Subjects: 639/301/119/2792; 639/301/119/544; 639/301/119/995; 639/925/357/1018; Carrier density; Channels; Condensed Matter Physics; Conductivity; Current carriers; Data analysis; Photoelectric emission; Physics; Physics and Astronomy; Quantum Physics; Structural Materials; Surfaces and Interfaces; Thin Films; Topological insulators; Topology; Transport properties
• ISSN: 2397-4648; 2397-4648
• DOI: 10.1038/s41535-018-0116-1

In the thin film limit, the surface state of a three-dimensional topological insulator gives rise to two parallel conduction channels at the top and bottom surface of the film, which are difficult to disentangle in transport experiments. Here, we present gate-dependent multi-tip scanning tunneling microscope transport measurements combined with photoemission experiments all performed in situ on pristine BiSbTe 3 thin films. To analyze the data, we develop a generic transport model including quantum capacitance effects. This approach allows us to quantify the gate-dependent conductivities, charge carrier concentrations, and mobilities for all relevant transport channels of three-dimensional topological insulator thin films (i.e., the two topological surface state channels, as well as the interior of the film). For the present sample, we find that the conductivity in the bottom surface state channel is minimized below a gate voltage of V gate  = −34 V and the top surface state channel dominates the transport through the film. Topological insulators: shedding light on parallel transport channels BiSbTe 3 is a promising topological insulator; the detailed transport properties of thin films of this material have now been reported. To study the electronic and transport properties of BiSbTe 3 films, Felix Lüpke at the Forschungszentrum Jülich in Germany and colleagues combined angle-resolved photoemission spectroscopy and gated four-tip scanning tunneling microscopy, gaining access to a comprehensive picture of the transport. A model developed specifically for this analysis enabled them to disentangle the transport occurring through the different channels (the surface state channels on the top and bottom of the sample and the bulk) and to obtain the gate-dependent conductivities, charge carrier concentrations, and mobilities. This combination of experimental techniques and data analysis is of general applicability and should prove useful for studying other samples.