Disorder-induced decoupled surface transport channels in thin films of doped topological insulators

Nonideal topological insulator (TI) films in which the bulk states are not insulating due to unintentional doping exhibit strong surface-bulk coupling. Such surface-bulk coupling can further induce intersurface coupling that affects the electrical conductivity of the TI films through a quantum interference effect known as weak antilocalization. Increased understanding and control of intersurface coupling is therefore crucial for the use of TI-based quantum devices. In this report on the transport properties of doped Bi2Se3 films under perpendicular and parallel magnetic fields, we observe a crossover between coupled and decoupled surface channels that is mediated by intentional disorder controlled by a post-annealing process. The intentional disorder causes the surface state carriers to rapidly lose their quantum phase and coherence, and as a result, more disordered Bi2Se3 films exhibit a shorter penetration depth of the surface state into the bulk states and weaker intersurface coupling, even though stronger surface-bulk coupling is expected. In previous studies, the role of disorder has generally been considered by determining its effect on surface-bulk scattering, but our results indicate that the role of disorder must be considered as a source of decoherence.