  The surface states of a 3D topological insulator (TI) exhibit topological
protection against backscattering. However, the contribution of bulk electrons
to the transport data is an impediment to the topological protection of
surface. We report the tuning of the chemical potential in the bulk of Bi2Se2Te
TI thin films, pinning it near the center of the bulk band gap, thereby
suppressing the bulk carriers. The temperature dependent resistance of these
films shows activated behavior down to 50K, followed by a metallic transition
at lower temperatures, a hallmark of the robustness of TI surface states.
Manifestation of topological protection and surface dominated transport is
explained by 2D weak antilocalization phenomenon. We further explore the effect
of surface to bulk coupling in TI in this work, which is captured by the number
of effective conducting surface channels that participate in the transport. The
presence of a single conducting channel indicates a strong surface to bulk
coupling which is detrimental to purely topological transport. We demonstrate
the decoupling of topological surface states on opposite surfaces of thin
films, thereby suppressing the bulk transport. Our findings provide a deeper
understanding of surface to bulk coupling along with topological transport
behavior and their respective tunability.
