Moiré superlattices and high-temperature surface superconductivity in the topological insulator Sb₂Te₃

Moiré superlattices formed by a relative twisting of abutting 2D layers can strongly impact the local electronic band structure in a variety of materials, inducing van Hove singularities, band gaps, minibands, and the recently discovered remarkable occurrence of superconductivity at T_c ~ 1.7 K in the magic-angle twisted bilayer graphene. In the vicinity of the magic angle, the periodic moiré potentials flatten the electronic bands, with electron correlations becoming strongly enhanced. Thus far only limited studies exist for moiré superlattices formed in 3D topological insulators (TIs), and the theoretical prediction [1] of moiré-induced high-T_c superconductivity in a 3D TI has not been experimentally confirmed. We have previously shown that a 2D superconductivity can be realized in a 3D TI Sb₂Te₃ [2], where the superconducting condensate emerges in surface Dirac puddles at a very high temperature of 55-60 K. Here, we demonstrate the existence of complex moiré-type superlattices in the thin exfoliated layers of this surface-superconducting Sb₂Te₃. The analysis of high-resolution transmission electron microscopy reveals a distribution of puddle sizes consistent with the ac susceptibility and scanning tunneling spectroscopy, and a skewed distribution of twist angle θ corresponding to hexagonal (θ ≤ 3°) and striped (θ ≥ 3°) moiré patterns. We corroborate our findings by density functional theory (DFT) calculations and discuss the association with high-T_c.