Gate control of surface transport in MBE-grown topological insulator (Bi _1-xSb _x) ₂Te ₃ thin films

Topological insulators are quantum materials comprised of an insulating bulk gap and topologically protected metallic surfaces with a Dirac-like band dispersion. To access the Dirac point by transport measurements is a very challenging issue faced in current investigations of these materials. Here we report the electronic state modulation in topological insulator (Bi _1-xSb _x) ₂Te ₃ thin films by means of an ionic-liquid gating. The films with 20 nm thickness were grown on lattice-matched semi-insulating InP substrates by molecular beam epitaxy; the temperature dependencies of resistance of these films clearly indicate their insulating bulk and metallic surface characteristics. The surface state carriers were systematically controlled by using electric-double-layer transistor (EDLT) configurations with ionic-liquid dielectrics. It was demonstrated that the surface state in the (Bi _1-xSb _x) ₂Te ₃-based EDLTs is tuned across the Dirac point, showing ambipolar transport in a topological transport regime.