Double layer of tunable graphene nanoribbons for enhancing absorption, reflection, or transmission

Graphene nanoribbons can exhibit high reflection for an incident wave even for an atom-size thickness. We show that in a double layer of graphene nanoribbons, highly efficient reflection, transmission, or absorption with each coefficient being higher than 0.9 can be obtained around the design frequency of 27 THz by properly setting the chemical potentials of the graphene nanoribbons for each case. High reflection in the system occurs due to the dominant contribution from the graphene nanoribbon layer close to the incident wave, while the system shows high transmission with each resonance frequency of the two graphene nanoribbon layers being away from the design frequency. Interestingly, high absorption arises from suppressing reflection and transmission by detuning the resonance frequency in one of the two graphene nanoribbon layers. In addition, the variation of the chemical potentials allows us to tune the resonance frequency of the electromagnetic responses. Our system shows a robust angular response due to the thin structure less than 0.05 free space wavelengths. We develop a coupled mode theory that elucidates the mechanism and captures the behavior observed in numerical results.