Independence of topological surface state and bulk conductance in three-dimensional topological insulators

The archetypical 3D topological insulators Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃ commonly exhibit high bulk conductivities, hindering the characterization of the surface state charge transport. The optimally doped topological insulators Bi₂Te₂Se and Bi_2-xSb_xTe₂S, however, allow for such characterizations to be made. Here we report an experimental comparison of the conductance for the topological surface and bulk states in Bi₂Te₂Se and Bi_1.1Sb_0.9Te₂S, based on temperature-dependent high-pressure measurements. We find that the surface state conductance at low temperature remains constant in the face of orders of magnitude increase in the bulk state conductance, revealing in a straightforward way that the topological surface states and bulk states are decoupled at low temperatures, consistent with theoretical models, and confirming topological insulators to be an excellent venue for studying charge transport in 2D Dirac electron systems.