Topological insulators (TI) are nominal gapped band insulators in the bulk, but have nontrivial, “topologically protected”, spin-helical conducting states with gapless Dirac fermion dispersion on the surface. Such “topological surface states” are considered promising platforms to explore various novel physics ranging from quantum anomalous Hall effect, Majorana fermions to excitonic condensation. However, electronic transport of topological surface states in real TI materials is easily obscured by competing conduction channels that include the bulk as well as the “conventional” 2D electron gas (2DEG) formed by band bending at the surface. This is a major challenge in current experiments and device applications involving topological insulators.
In this talk, I will describe our recent charge and spin transport experiments on TI materials based on Bi2Se3, Bi2Te3 and Bi2Te2Se. We have explored ways to reduce the bulk conduction, and revealed a list of unique electronic transport signatures of the spin-helical, Dirac fermion topological surface states. In addition, we have also observed interesting transport phenomena attributed to the bulk and “conventional” surface 2DEG that demonstrate the complex electronic properties in real TI materials. These experiments may facilitate better access and control of TI surface states to explore the more exotic physics and applications in topological quantum devices.