A moir\'e superlattice on the surface of a topological insulator

TL;DR

This paper theoretically explores how a moiré superlattice affects the surface Dirac cone of a topological insulator, revealing velocity renormalization, satellite Dirac cones, and topological constraints on band gaps.

Contribution

It provides a detailed theoretical analysis of moiré effects on topological insulator surfaces, highlighting the role of bulk topology and predicting new surface band phenomena.

Findings

Surface Dirac cone velocity is dramatically renormalized.

Topological constraints prevent the opening of surface band gaps.

Emergence of satellite Dirac cones that can be flat and anisotropic.

Abstract

Twisting van der Waals heterostructures to induce correlated many-body states provides a novel tuning mechanism in solid-state physics. In this work, we theoretically investigate the fate of the surface Dirac cone of a three-dimensional topological insulator subject to a superlattice potential. Using a combination of diagrammatic perturbation theory, lattice model simulations, and ab initio calculations we elucidate the unique aspects of twisting a single Dirac cone with an induced moir\'e potential and the role of the bulk topology on the reconstructed surface band structure. We report a dramatic renormalization of the surface Dirac cone velocity as well as demonstrate a topological obstruction to the formation of isolated minibands. Due to the topological nature of the bulk, surface band gaps cannot open; instead, additional satellite Dirac cones emerge, which can be highly anisotropic and made quite flat. We discuss the implications of our findings for future experiments.