The unchanged top surface-state structures in three-dimensional topological insulator Sb₂Te₃ thin films in the presence of bottom-surface Moiré potentials

The exertion of a long-period potential on two-dimensional (2D) systems leads to bandstructure downfolding and the formation of mini flat bands, thereby providing a route for band engineering and enabling the realization of new physical phenomena through the tuning of electron-electron interactions. In this work, the effect of the Moiré superlattice formed between the substrate and the bottom quintuple layer (QL) of 3- and 4-QL three-dimensional (3D) topological insulator Sb 2 Te 3 thin films on the top surface states was investigated. The scanning tunneling spectra reveal that the bulk-like bands exhibit potential variations consistent with the Moiré pattern. In contrast, the surface states display only minimal potential variations, resulting in the absence of mini-band formation in the top surface states. These surface states remain nearly unaffected, as confirmed by Landau-level spectroscopy and simulations. The results suggest distinct roles of the bottom-surface Moiré potential on the bulk states and the top surface states in the weak coupling regime between the two surfaces.