Strain effect on the optical conductivity of graphene

TL;DR

This paper investigates how uniaxial strain affects the electronic band structure and optical conductivity of graphene, revealing strain-induced band gaps and topological transitions that influence optical properties.

Contribution

It provides a detailed analysis of strain effects on graphene's electronic and optical properties, including the emergence of band gaps and topological changes, within a tight binding framework.

Findings

Band gap opens under intense strain

Topological transition of Fermi line occurs

Optical conductivity varies with strain and direction

Abstract

Within the tight binding approximation, we study the dependence of the electronic band structure and of the optical conductivity of a graphene single layer on the modulus and direction of applied uniaxial strain. While the Dirac cone approximation, albeit with a deformed cone, is robust for sufficiently small strain, band dispersion linearity breaks down along a given direction, corresponding to the development of anisotropic massive low-energy excitations. We recover a linear behavior of the low-energy density of states, as long as the cone approximation holds, while a band gap opens for sufficiently intense strain, for almost all, generic strain directions. This may be interpreted in terms of an electronic topological transition, corresponding to a change of topology of the Fermi line, and to the merging of two inequivalent Dirac points as a function of strain. We propose that these features may be observed in the frequency dependence of the longitudinal optical conductivity in the visible range, as a function of strain modulus and direction, as well as of field orientation.