Structural classification of boron nitride twisted bilayers and ab initio investigation of their stacking-dependent electronic structure

TL;DR

This paper classifies the stacking configurations of boron nitride twisted bilayers and uses ab initio methods to analyze how their electronic structures vary with twist angle and stacking, revealing conserved features.

Contribution

It introduces a new classification and nomenclature for boron nitride bilayer stackings and studies their electronic properties using density functional theory.

Findings

Five distinct stacking types for given moiré periodicity

The band gap remains indirect across all angles and stackings

Certain electronic features are conserved within the same stacking sequence

Abstract

Since the discovery of superconductive twisted bilayer graphene which initiated the field of twistronics, moir\'e systems have not ceased to exhibit fascinating properties. We demonstrate that in boron nitride twisted bilayers, for a given moir\'e periodicity, there are five different stackings which preserve the monolayer hexagonal symmetry (i.e. the invariance upon rotations of 120$^\circ$) and not only two as always discussed in literature. We introduce some definitions and a nomenclature that identify unambiguously the twist angle and the stacking sequence of any hexagonal bilayer with order-3 rotation symmetry. Moreover, we employ density functional theory to study the evolution of the band structure as a function of the twist angle for each of the five stacking sequences of boron nitride bilayers. We show that the gap is indirect at any angle and in any stacking, and identify features that are conserved within the same stacking sequence irrespective of the angle of twist.