Misalignment instability in magic-angle twisted bilayer graphene on hexagonal boron nitride

Abstract

We study the stability and electronic structure of magic-angle twisted bilayer graphene on the hexagonal boron nitride (TBG/BN). Full relaxation has been performed for commensurate supercells of the heterostructures with different twist angles (${\theta }^{\prime }$) and stackings between TBG and BN. We find that the slightly misaligned configuration with ${\theta }^{\prime }=0.54^{\circ }$ and the AA/AA stacking has the globally lowest total energy due to the constructive interference of the moiré interlayer potentials and thus the greatly enhanced relaxation in its $1\times 1$ commensurate supercell. Gaps are opened at the Fermi level ($E_F$) for small supercells with the stackings that enable strong breaking of the $C_2$ symmetry in the atomic structure of TBG. For large supercells with ${\theta }^{\prime }$ close to those of the $1\times 1$ supercells, the broadened flat bands can still be resolved from the spectral functions. The ${\theta }^{\prime }=0.54^{\circ }$ is also identified as a critical angle for the evolution of the electronic structure with ${\theta }^{\prime }$, at which the energy range of the mini-bands around $E_F$ begins to become narrower with increasing ${\theta }^{\prime }$ and their gaps from the dispersive bands become wider. The discovered stablest TBG/BN with a finite ${\theta }^{\prime }$ of about $0.54^{\circ }$ and its gapped flat bands agree with recent experimental observations.

8 pages, 6 figures

References in corpus (7)

• Lattice relaxation and energy band modulation in twisted bilayer graphenes
• Origin of band gaps in graphene on hexagonal boron nitride
• The crucial role of atomic corrugation on the flat bands and energy gaps of twisted bilayer graphene at the "magic angle" $\theta \sim 1.08^{\circ }$
• Continuum models for twisted bilayer graphene: the effects of lattice deformation and hopping parameter
• Structure of twisted and buckled bilayer graphene
• Moiré band model and band gaps of graphene on hexagonal boron nitride
• Symmetry breaking in the double moiré superlattices of relaxed twisted bilayer graphene on hexagonal boron nitride

Cited by in corpus (1)

• Quasiperiodicity, band topology, and moiré graphene