Coherent transport in density-tunable topological surface states in Bi2Se3

I will present our studies of electronic transport in the density-tunable surface states of the Topological Insulator (TI) Bi₂Se₃. TI surface states, intensively studied by ARPES and STM, pose a challenge for transport experiments due to parallel conduction through bulk states, limited surface density tunability, and uncertainty in the surface-to-bulk coupling. To single out the surface transport we study thin devices (<100 nm) fabricated by two different approaches: (i) Bi₂Se₃ flakes exfoliated from single crystals¹; (ii) Devices patterned from evaporated thin films. In the thin film devices transport is dominated by the surface states, and exhibits pronounced ambipolar resistance modulation².

The TI devices exhibit an unusual weak-antilocalization correction to conductance, which appears to be carried by multiple coherently-independent channels. The effective number of independent channels depends on the voltage of the density-tuning gate, on temperature, and on the bulk doping. We suggest that this is a consequence of tunable surface-to-bulk coupling, and that our results provide an indication that the surface state individually exhibits the weak-antilocalization correction, as expected from its chiral properties.

^{1. Surface State Transport and Ambipolar Electric Field Effect in Bi2Se3 Nanodevices. H. Steinberg, D. Gardner, Y. Lee & P. Jarillo-Herrero. Nano Letters 10, 5032-5036 (2010).}

^{2. Electrically tunable surface-to-bulk coherent coupling in topological insulator thin films. H. Steinberg, J.-B. Laloë, V. Fatemi, J.-S. Moodera & P. Jarillo-Herrero. arXiv:1104.1404 (2011).}