Thickness-independent transport channels in topological insulator Bi2Se3 thin films

With high quality topological insulator (TI) Bi2Se3 thin films, we report thickness-independent transport properties over wide thickness ranges. Conductance remained nominally constant as the sample thickness changed from 256 to ~8 QL (QL: quintuple layer, 1 QL = ~1 nm). Two surface channels of very different behaviors were identified. The sheet carrier density of one channel remained constant at ~3.0 x 10^13 cm^-2 down to 2 QL, while the other, which exhibited quantum oscillations, remained constant at ~8 x 10^12 cm^-2 only down to ~8 QL. The weak antilocalization parameters also exhibited similar thickness-independence. These two channels are most consistent with the topological surface states and the surface accumulation layers, respectively.