Emergence of flat bands in the quasicrystal limit of boron nitride twisted bilayers

Abstract

We investigate the electronic structure and the optical absorption onset of close-to-30\degree twisted hexagonal boron nitride bilayers. Our study is carried out with a purposely developed tight-binding model validated against DFT simulations. We demonstrate that approaching 30\degree (quasicrystal limit), all bilayers sharing the same moiré supercell develop identical band structures, irrespective of their stacking sequence. This band structure features a bundle of flat bands laying slightly above the bottom conduction state which is responsible for an intense peak at the onset of the absorption spectrum. These results suggest the presence of strong, stable and stacking-independent excitons in boron nitride 30\degree-twisted bilayers. By carefully analyzing the electronic structure and its spatial distribution, we elucidate the origin of these states as moiré-induced K-valley scattering due to interlayer B$-$B coupling. We take advantage of the the physical transparency of the tight-binding parameters to derive a simple triangular model based on the B sublattice that accurately describes the emergence of the bundle. Being our conclusions very general, we predict that a similar bundle should emerge in other close-to-30{\degree} bilayers, like transition metal dichalcogenides, shedding new light on the unique potential of 2D materials.

References in corpus (15)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Many-body perturbation theory calculations using the yambo code
• Numerical studies of confined states in rotated bilayers of graphene
• Superconductivity and strong interactions in a tunable moiré quasiperiodic crystal
• Electrically tunable valley dynamics in twisted WSe${}_2$/WSe${}_2$ bilayers
• Quasicrystalline electronic states in 30${}^{\circ }$ rotated twisted bilayer graphene
• An accurate description of the structural and electronic properties of twisted bilayer graphene-boron nitride heterostructures
• Electronic localization in twisted bilayer MoS${}_2$ with small rotation angle
• Flat bands, strains, and charge distribution in twisted-bilayer hBN
• Flat bands and chiral optical response of moiré insulators
• Magic angles in twisted bilayer graphene near commensuration: Towards a hypermagic regime
• Two limit cases of twisted hBN bilayers and their excitonic response
• Excitons in twisted AA' hexagonal boron nitride bilayers
• Quantum Valley and Sub-valley Hall Effect in the Large Angle Twisted Bilayer Graphene

Cited by in corpus (4)

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• Electronic structure and transport in materials with flat bands: 2D materials and quasicrystals
• Twisting in h-BN bilayers and their angle-dependent properties
• Review of the tight-binding method applicable to the properties of moiré superlattices