Tunable crystal symmetry in graphene–boron nitride heterostructures with coexisting moiré superlattices

• Published in: Nature nanotechnology Vol. 14; no. 11; pp. 1029 - 1034
• Main Authors: Finney, Nathan R., Yankowitz, Matthew, Muraleetharan, Lithurshanaa, Watanabe, K., Taniguchi, T., Dean, Cory R., Hone, James
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2019; Nature Publishing Group
• Subjects: 140/133; 639/766/119/1000/1018; 639/766/119/995; Alignment; Band structure of solids; Boron; Boron nitride; Chemistry and Materials Science; Composite materials; Crystal lattices; Crystals; Graphene; Heterostructures; Letter; Materials Science; Nanotechnology; Nanotechnology and Microengineering; optics, defects, charge transport, superconductivity, magnetism and spin physics, mesoscale science, materials and chemistry by design, mesostructured materials, synthesis (novel materials), synthesis (self-assembly); Superlattices; Symmetry; Wavelength
• ISSN: 1748-3387; 1748-3395; 1748-3395
• DOI: 10.1038/s41565-019-0547-2

In van der Waals (vdW) heterostructures consisting of atomically thin crystals layered on top of one another, lattice mismatch and rotation between the layers can result in long-wavelength moiré superlattices. These moiré patterns can drive notable band structure reconstruction of the composite material, leading to a wide range of emergent phenomena including superconductivity 1 – 3 , magnetism 4 , fractional Chern insulating states 5 and moiré excitons 6 – 9 . Here, we investigate devices consisting of monolayer graphene encapsulated between two crystals of boron nitride (BN), in which the rotational alignment of all three components is controlled. We find that bandgaps in the graphene arising from perfect rotational alignment with both BN layers can be modified considerably depending on whether the relative orientation of the two BN layers is 0° or 60°, suggesting a tunable transition between the absence or presence of inversion symmetry in the heterostructure. Small deviations (<1°) from perfect alignment of all three layers leads to coexisting long-wavelength moiré potentials, resulting in a highly reconstructed graphene band structure featuring multiple secondary Dirac points. Our results demonstrate that the interplay between multiple moiré patterns can be utilized to controllably modify the symmetry and electronic properties of the composite heterostructure. Engineering multiple moiré patterns within a boron nitride–graphene–boron nitride heterostructure enables tunable crystal symmetry and strong modification of the graphene band structure.