Comment on "Gap opening in graphene by shear strain"

TL;DR

This paper critiques a previous study claiming that shear and uniaxial strain can open a band gap in graphene, showing that when buckling and wrinkling are considered, the band gap disappears and graphene remains gapless.

Contribution

The study demonstrates that buckling and wrinkling effects negate the previously predicted band gap opening in strained graphene.

Findings

Band gap predicted at 15-20% shear strain vanishes when buckling is considered.

Graphene remains gapless under large shear and combined strains.

Mechanical effects like buckling are crucial in electronic structure predictions.

Abstract

G. Cocco, E. Cadelano, and L. Colombo [Phys. Rev. B 81, 241412(R) (2010)] have suggested that combinations of shear and uniaxial strain can be used to open a band gap in graphene at much lower levels of strain than with the application of unaxial strain alone. They employed a unit cell of graphene in their studies and applied the Cauchy-Born rule to model external strain. Consequently, an important aspect of the mechanical behavior of membranes, namely buckling and wrinkling under external strain, and the attendant coupling with electronic structure was ignored in their analysis. Upon doing so, the apparent band gap that appears in the range of 15-20% shear strain under the Cauchy-Born assumption is shown to vanish. The gapless spectrum of graphene is found to persist under large shear strains as well as large combinations of shear and uniaxial strain.