Strain-induced stacking transition in bilayer graphene

TL;DR

This study uses DFT calculations to show that applying small strains (~1%) to bilayer graphene can reversibly alter its stacking order, offering a new way to engineer electronic properties without twisting layers.

Contribution

It demonstrates how external heterostrain influences stacking transitions in bilayer graphene, providing insights into strain-induced control of electronic structure.

Findings

Strain above ~1% favors unstrained free layer

Critical strain disrupts AB-stacking, leading to mixed stacking

Small strains enable reversible stacking engineering

Abstract

Strain, both naturally occurring and deliberately engineered, can have a considerable effect on the structural and electronic properties of 2D and layered materials. Uniaxial or biaxial heterostrain modifies the stacking arrangement of bilayer graphene (BLG) which subsequently influences the electronic structure of the bilayer. Here, we use Density Functional Theory (DFT) calculations to investigate the interplay between an external applied heterostrain and the resulting stacking in BLG. We determine how a strain applied to one layer is transferred to a second, 'free' layer and at what critical strain the ground-state AB-stacking is disrupted. To overcome limitations introduced by periodic boundary conditions, we consider an approximate system consisting of an infinite graphene sheet and an armchair graphene nanoribbon (AGNR). We find that above a critical strain of ~1%, it is energetically favourable for the free layer to be unstrained, indicating a transition between uniform AB-stacking and non-uniform mixed stacking. This is in agreement with a simple model estimate based on the individual energy contributions of strain and stacking effects. Our findings suggest that small levels of strain provide a platform to reversibly engineer stacking order and Moir\'e features in bilayers, providing a viable alternative to twistronics to engineer topological and exotic physical phenomena in such systems.