Moir\'e Periodic and Quasiperiodic Crystals in Heterostructures of Twisted Bilayer Graphene and Hexagonal Boron Nitride

TL;DR

This paper explores how stacking two atomic crystals with a twist creates tunable moiré and quasiperiodic structures, revealing new electronic phases and self-alignment phenomena in twisted bilayer graphene on hBN.

Contribution

It introduces a new class of tunable double moiré quasiperiodic structures, including quasicrystals with forbidden symmetries, expanding the understanding of moiré physics.

Findings

Observation of a wide range of commensurate and incommensurate moiré phases.

Identification of quasicrystals with dodecagonal symmetry.

Discovery of an unexpected self-alignment mechanism in moiré structures.

Abstract

Stacking two atomic crystals with a twist between their crystal axes produces moir\'e potentials that modify the electronic properties. Here we show that double moir\'e potentials generated by superposing three atomic crystals create a new class of tunable quasiperiodic structures that alter the symmetry and spatial distribution of the electronic wavefunctions. By using scanning tunneling microscopy and spectroscopy to study twisted bilayer graphene on hexagonal boron nitride (hBN), we unveil a moir\'e phase diagram defined by the lattice constants of the two moir\'e lattices (graphene-on-graphene and graphene-on-hBN), comprising both commensurate periodic and incommensurate quasiperiodic crystals. Remarkably, the 1:1 commensurate crystal, which should theoretically exist at only one point on this phase diagram, is observed over a wide range, demonstrating an unexpected self-alignment mechanism. The incommensurate crystals include quasicrystals, which are quasiperiodic and feature a Bravais-forbidden dodecagonal symmetry, and intercrystals, which are also quasiperiodic but lack forbidden symmetries. This rich variety of tunable double moir\'e structures offers a synthetic platform for exploring the unique electronic properties of quasiperiodic crystals, which are rarely found in nature.