Disorder-induced decoupled surface transprot channels in thin films of doped topological insulator*

Non-ideal topological insulator film that the bulk states are not insulating due to unintentional doping reveals strong surface-bulk coupling. Furthermore, the surface-bulk coupling can induce the inter-surface coupling which affects the quantum interference effect on electrical conductivity known as weak anti-localization. Therefore, interpretation and control of the inter-surface coupling are important to utilize the TI-based quantum devices. In this report, from the transport studies of doped Bi₂Se₃ films under the perpendicular and parallel magnetic field, we observe the crossover between coupled and decoupled surface channels through intentional disorder controlled by a post-annealing process. The intentional disorder makes that the carriers of surface state rapidly lose their quantum phase and coherence. Consequently, the more disordered Bi₂Se₃ film reveals shorter penetration depth of the surface state into the bulk states and weaker inter-surface coupling even though it is expected stronger surface-bulk coupling.