Strain-Modulated Graphene Heterostructure as a Valleytronic Current Switch

TL;DR

This paper develops a detailed theoretical model for strained graphene, showing how strain can be used to control electronic transmission and achieve high ON-OFF ratios and valley polarization in graphene heterostructures.

Contribution

It introduces a comprehensive tight-binding Hamiltonian for strained graphene, including previously neglected strain effects, and demonstrates their impact on electronic transport properties.

Findings

High ON-OFF ratios up to 10^12 predicted

Strain modulation enables control of valley polarization

Transmission can be tuned by strain magnitude and direction

Abstract

Strain engineering is a promising approach for suppressing the OFF-state conductance in graphene-based devices that arises from Klein tunnelling. In this work, we derive a comprehensive tight-binding Hamiltonian for strained graphene that incorporates strain-induced effects that have been neglected hitherto, such as the distortion of the unit cell under strain, the effect of strain on the next-nearest neighbor coupling, and the second-order contributions of the strain tensor. We derive the corresponding low-energy effective Hamiltonian about the Dirac points and reformulate the boundary conditions at the interfaces between strained and unstrained graphene in light of additional terms in the Hamiltonian. By applying these boundary conditions, we evaluate the transmission across a strained graphene heterostructure consisting of a central segment sandwiched between two unstrained leads. Modulation of the transmitted current can be effected by varying the magnitude and direction of the applied strain, as well as by the applying a gate voltage. Based on realistic parameter values, we predict that high ON-OFF ratios of up to $10^{12}$ as well as high current valley polarization can be achieved in the strain-modulated device.