Dynamically Tunable Extraordinary Light Absorption in Monolayer Graphene

Graphene due to the absence of bandgap and monolayer thickness exhibits very weak light absorption in the visible to IR frequencies, which prevents being an efficient optical material. Here, we show theoretically as well as experimentally that the excitation of cavity coupled surface plasmons directly on graphene enhances absorbance up to 60% with low damping rate in both high and low mobility graphene. This result is based on the principle that the cavity and the surface plasmon concentrate the energy of the incident electromagnetic wave at the location of the graphene sheet. The advantages of graphene is the ease of electrical tunability of plasmon resonance frequency, the high degree of electric field confinement, and the low plasmon damping rate due to the high carrier mobility in graphene. Constructive interference between incident and scattered electric fields strengthens total electric field on the graphene nanomesh by coupling the perforated graphene to an optical cavity. In this work, the effects of carrier mobility and electron-phonon coupling have been studied experimentally and theoretically. It is shown that the plasmon-phonon coupling leads to the renormalization of the plasmonic dispersion relation.