Strain- and doping-tunable optical resonance in Kekul\'e-Y graphene

Abstract

We investigate the optical response of Kekul\'e-Y graphene under uniaxial strain and carrier doping. Using a low-energy effective Hamiltonian, we show that strain reshapes the low-energy electronic structure of the Kekul\'e-Y phase and induces Van Hove singularities at energies well below those of pristine graphene. Within the Kubo formalism, we calculate the optical conductivity and identify multiple anisotropic interband features, with a pronounced resonance arising from strain-induced Van Hove singularities. The pronounced resonance is strongly anisotropic and robust against moderate thermal broadening and disorder, providing a clear optical signature of Kekul\'e-Y ordering. We further derive analytical expressions for the low-energy optical conductivity and the Drude weight, providing a detailed characterization of the strain- and doping-dependent optical response. Our results establish strain engineering as an effective route for controlling valley-dependent optical properties in Kekul\'e-Y graphene, originating from the Kekul\'e-induced coupling of the Dirac valleys, and suggest feasible optical probes for the experimental identification of the Kekul\'e-Y phase.