Abstract
Recently, moiré superlattices have been found on the surface of topological insulators due to the rotational misalignment of topmost layers. In this work, we study the effects of moiré superlattices on the topological surface states using a continuum model of Dirac electrons moving in a periodic potential. Unlike twisted bilayer graphene, moiré surface states cannot host isolated bands due to their topological nature. Instead, we find (high-order) van Hove singularities (VHS) in the moiré band structure that give rise to divergent density of states (DOS) and enhance interaction effects. Because of spin-momentum locking in moiré surface states, possible interaction channels are limited. In the presence of phonon mediated attraction, superconductivity is strongly enhanced by the power-law divergent DOS at high-order VHS. The transition temperature exhibits a power-law dependence on the retarded electron-phonon interaction strength . This enhancement is found to be robust under various perturbations from the high-order VHS.
- Received 27 October 2020
- Revised 9 February 2021
- Accepted 9 March 2021
DOI:https://doi.org/10.1103/PhysRevX.11.021024
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
When two adjacent atomic layers are slightly misaligned, a long-wavelength geometric structure known as a moiré pattern emerges, which can lead to new and surprising electronic behavior. A famous example is twisted bilayer graphene, which exhibits superconductivity and other correlated effects. In this work, we consider the moiré pattern formed on surfaces of topological insulators—materials that are insulators in their interiors and yet conduct electricity on their surfaces, which feature unique electron states unlike any found on other 2D materials.
To study how a moiré pattern on the surface of a topological insulator might impact its electronic behavior, we construct a computational model based on electrons moving through a periodic potential. From this, we find that the electronic structure on the topological insulator surface with moiré patterns differs fundamentally from those found in usual moiré materials. We further reveal that the moiré pattern at certain “magic angles” could lead to topological superconductivity at temperatures up to about 10 K.
Our work explores how topology and moiré physics intertwine and lead to exotic superconductivity. In the future, we will keep exploring how this intertwinement leads to new physics.
