Moir\'e flat bands and antiferroelectric domains in lattice relaxed twisted bilayer hexagonal boron nitride under perpendicular electric fields

TL;DR

This study investigates moiré flat bands and antiferroelectric domains in lattice-relaxed twisted bilayer hexagonal boron nitride under perpendicular electric fields, revealing how twist angle and electric fields influence charge polarization and electronic properties.

Contribution

It provides a detailed analysis of charge polarization, band width, and electrostatic potential variations in twisted bilayer hBN, incorporating lattice relaxation effects and electric field dependence, which were not previously characterized.

Findings

Flat bands with widths less than 1 meV for angles below 1.08° (BN/BN) and 1.5° (BN/NB)

Charge polarization maxima of 2.6 pC/m at AB/BA sites, evolving with twist angle

Electrostatic potential is enhanced by 20% compared to rigid models

Abstract

Local interlayer charge polarization of twisted bilayer hexagonal boron nitride (t2BN) is calculated and parametrized as a function of twist angle and perpendicular electric fields through tight-binding calculations on lattice relaxed geometries Lattice relaxations tend to increase the bandwidth of the nearly flat bands, where widths smaller than 1 meV are expected for angle less than 1.08 degree for parallel BN/BN alignment, and for angle less than 1.5 degree for the antiparallel BN/NB alignment. Local interlayer charge polarization maxima of 2.6 pC/m corresponding are expected at the AB and BA stacking sites of BN/BN aligned t2BN in the long moire period limit for angle less than 1 degree, and evolves non-monotonically with a maximum of 3.5 pC/m at angle equal to 1.6 degree before reaching 2 pC/m for angle equal to 6 degree. The electrostatic potential maxima due to the t2BN are overall enhanced by 20 percentage with respect to the rigid system assuming potential modulation depths of up to 300 mV near its surface. In BN/BN aligned bilayers the relative areas of the AB or BA local stacking regions can be expanded or reduced through a vertical electric field depending on its sign.