Strain-Modulated Graphene Heterostructure as a Valleytronic Current Switch

Abstract

Strain engineering is a promising approach for suppressing the off-state conductance in graphene-based devices that arises from Klein tunneling. 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 application of 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.