Transition from Surface to Hopping Conduction in Stacked Nonepitaxial Bi₂Se₃ Dual Thin Films

We investigate quantum transport in topological insulators through nonepitaxial thin film stacking. A KOH-(potassium hydroxide)-assisted mechanical transfer is developed for fabricating stacked nonepitaxial Bi₂Se₃ dual thin films. While deliberate rotational misalignment is introduced during stacking, X-ray diffraction confirms the preservation of crystallinity and strong c-axis orientation. Single thin-film samples exhibit a metallic-to-activated transition near 130 K, indicative of surface-dominated transport. In contrast, the dual thin-film stack shows a nonmonotonic resistance minimum at 50 K, followed by an upturn well described by a three-dimensional variable-range hopping model (R ² ≈ 0.98), suggesting disorder-driven localization. Magnetotransport measurements further reveal suppressed linear magnetoresistance and enhanced weak antilocalization, indicating disrupted surface coherence due to interfacial hybridization. These results demonstrate that stacking-induced disorder fundamentally alters the transport regime, favoring hopping conduction over coherent surface states. This work provides a platform for engineering quantum transport through nonepitaxial stacking in topological systems.