Plasmon Resonances in a Periodic Square Coaxial Hole Array in a Graphene Sheet

We present a computational study of the plasmon resonances in a periodic square coaxial hole array in a graphene sheet, which consists of a square hole array and a square strip array. According to charge oscillation picture, we find that a new plasmon mode, which locates on the edges of square hole along the polarization direction of incident light, emerges in our proposed structure. Two hybridized plasmon resonance modes (i.e., symmetric and asymmetric plasmon resonance modes) are formed due to two different manners of coupling between the new plasmon mode of square hole and the plasmon mode of square strip. The two plasmon resonance modes can be tuned over a wide wavelength range by a small change in the chemical potential of graphene. Furthermore, the two plasmon resonances can also be controlled by changing L (x) and L (y) (which are the strip offsets from the hole center perpendicular and parallel to the polarization direction of incident light, respectively), originating from the change in the strength of electromagnetic coupling between square hole and square strip. Our study gives an insight into the physical mechanism of plasmon resonances in square graphene coaxial hole array, and our findings will be useful for designing graphene-based plasmonic devices and metamaterials.