Tight-Binding Terahertz Plasmons in Chemical-Vapor-Deposited Graphene

Transistor structures comprising graphene and subwavelength metal gratings hold great promise for plasmon-enhanced terahertz detection. Despite considerable theoretical effort, little experimental evidence for terahertz plasmons in such structures has been found so far. Here we report an experimental study of plasmons in graphene-insulator-grating structures using Fourier-transform spectroscopy in the 5-10-THz range. The plasmon resonance is clearly visible above the Drude absorption background even in chemical-vapor-deposited graphene with low carrier mobility of approximately 10³ cm²/V s. We show that the plasmon lifetime exceeds the transport relaxation time extracted from dc mobility, and argue that the former is weakly sensitive to scattering by grain boundaries and macroscopic defects inherent in chemical-vapor-deposited samples. We find that a grating coupler close to graphene strongly modifies the plasmon spectrum, which is determined by metal stripe width but not by grating period. We present a simple theory of grating-coupled two-dimensional plasmons, akin to the tight-binding theory of electrons in solids, that reproduces the observed resonant frequencies without fitting parameters. Our results demonstrate the prospect of large-area commercially available graphene for resonant terahertz detectors.