Shear-Strain Controlled High-Harmonic Generation in Graphene

Two-dimensional Dirac electrons in single-layer graphene have attracted much attention for their novel linear and nonlinear optical properties. One-atom-thick graphene exhibits universal frequency-independent light absorption πα=2.3%, where α=e²⁄ℏc≈1/137 is the fine structure constant [1], and the ultrafast carrier dynamics in the massless Dirac bands enable a wide range of high-speed broadband optical responses. Recent studies have aimed to artificially control these properties for graphene-based optical devices. However, the robustness of optical transition probability πα inherent to 2D Dirac electrons makes the external control of linear and nonlinear optical responses highly challenging.

In this presentation [2], we propose a method for controlling the high-harmonic generation (HHG) with a high dynamic range in single-layer graphene. We find that, by utilizing shear strain, a significant enhancement or quenching of HHG is possible over a range of several orders of magnitude. This feature is made possible by the resonance mechanism at a van Hove singularity. Therein, the shear strain controls the configurations of the two Dirac cones, resulting in changes in the energy and dipole moment at the saddle point of the band dispersion. Our findings provide a way for modulating or switching light by using a nano-optomechanical device composed of single-layer graphene.