Experimental study of graphene-based plasmonic crystals in a strong-coupling regime

We have fabricated a large-area graphene-based transistor with top metal grating, which represents plasmonic crystal containing two-dimensional electron system gated by periodic metal grating. Using Fourier-transform infrared spectroscopy, we have studied the graphene plasmon modes in transmission spectra, which were efficiently excited by the incident light with the perpendicular polarization to metal grating. We have researched the dependence of resonance frequency of graphene plasmons on the bottom gate voltage. Here we demonstrate that excited graphene plasmons are strongly coupled to top metal grating and have the linear dispersion. These results not only prove the previous theoretical works but also demonstrate the possibility of significant reducing photon wavelength which can be controlled by modulating the carrier density of graphene via electrical gating. This result is important for design of highly effective tunable terahertz and far-infrared detectors.