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

Felix Lüpke,Detlev Grützmacher,Markus Eschbach,Peter Schüffelgen,Gregor Mussler,Ewa Młyńczak,Tristan Heider,Daniel Rosenbach,Lukasz Plucinski,Nils Von Den Driesch,Claus M Schneider,Martin Lanius,Bert Voigtländer,F Stefan Tautz,Vasily Cherepanov,Sven Just

doi:10.1038/s41535-018-0116-1

Abstract

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 BiSbTe3 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 Vgate = −34 V and the top surface state channel dominates the transport through the film.

Highlights

angle-resolved photoemission spectroscopy (ARPES) results obtained at hv = 8.4 eV are shown in Fig. 1b, c
1234567890():,; Fig. 1 Schematic of the measurement geometry and results obtained by photoemission spectroscopy and four-probe measurements. a Measurement setup consisting of a BiSbTe3 thin film grown on a silicon-on-insulator substrate
The tips of a four-tip scanning tunneling microscope contact the thin film surface while a gate voltage Vgate is applied to the back side of the substrate. b ARPES measurement of the k||,x/k||,y plane at the Fermi energy with a fit to the Fermi surface, without gating. c Corresponding photoemission intensity as a function of binding energy in k||,x direction with the Dirac cone indicated by dotted red lines. d In situ four-probe I/V measurement of the TI film. e Scanning electron microscopy image of the four-probe setup with equidistant tip spacing

Summary

INTRODUCTION

Understanding the behavior of topological insulators under the influence of an electric field is of fundamental interest for the application of the unique electronic properties of their topological surface states (TSS) in future electronic devices.[1,2] Among the most promising three-dimensional topological insulators (3D-TI). We use a combination of angle-resolved photoemission spectroscopy (ARPES) and gated four-tip scanning tunneling microscopy (STM) to characterize the electronic and transport properties of pristine epitaxial BiSbTe3 thin films under ultra-high vacuum (UHV) conditions. This approach gives us direct access to the filling level of the TSS at the surface of the same sample on which we perform transport measurements. We are able to describe the experimental data and determine the carrier concentrations and carrier mobilities in each of the three transport channels

RESULTS

DISCUSSION

METHODS