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 band-structure 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 Sb₂Te₃ thin films on the top surface states is 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.