Strain and field modulation in bilayer graphene band structure

TL;DR

This paper investigates how strain and electric fields influence the band structure of bilayer graphene, revealing that interlayer distance critically affects bandgap modulation, transition from direct to indirect bandgap, and saturation behavior.

Contribution

The study provides a detailed analysis of strain effects on bilayer graphene's bandgap modulation using extended Huckel theory, highlighting the impact of interlayer distance on electronic properties.

Findings

Higher bandgap modulation with reduced interlayer distance.

Transition from direct to indirect bandgap at ~2.5 Å interlayer distance.

Saturation of bandgap at high electric fields depending on interlayer distance.

Abstract

Using an external electric field, one can modulate the bandgap of Bernal stacked bilayer graphene by breaking A-~B symmetry. We analyze strain effects on the bilayer graphene using the extended Huckel theory and find that reduced interlayer distance results in higher bandgap modulation, as expected. Furthermore, above about 2.5 angstrom interlayer distance, the bandgap is direct, follows a convex relation to electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 angstrom, the bandgap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.