Gap opening in graphene by simple periodic inhomogeneous strain

TL;DR

This study demonstrates that simple periodic inhomogeneous strain can induce a significant electronic gap in graphene without electrostatic gating, challenging previous tight-binding predictions and revealing a threshold-dependent gap opening.

Contribution

The paper provides ab-initio evidence that inhomogeneous strain can open a sizable gap in graphene, contrasting with prior tight-binding models and identifying a threshold behavior.

Findings

Inhomogeneous strain opens a ~0.5 eV gap in graphene.

Gap opening occurs only when the strain amplitude-to-period ratio exceeds ~0.1.

Gap formation depends on preserving inversion symmetry, not on pseudo-magnetic fields.

Abstract

Using ab-initio methods, we show that the uniform deformation either leaves graphene (semi)metallic or opens up a small gap yet only beyond the mechanical breaking point of the graphene, contrary to claims in the literature based on tight-binding (TB) calculations. It is possible, however, to open up a global gap by a sine-like one-dimensional inhomogeneous deformation applied along any direction but the armchair one, with the largest gap for the corrugation along the zigzag direction (~0.5 eV) without any electrostatic gating. The gap opening has a threshold character with very sharp rise when the ratio of the amplitude A and the period of the sine wave deformation lambda exceeds (A/lambda)_c ~0.1 and the inversion symmetry is preserved, while it is threshold-less when the symmetry is broken, in contrast with TB-derived pseudo-magnetic field models.