Graphene Plasmonics for Tunable Terahertz Metamaterials

Plasmons describe collective oscillations of electrons. They have a fundamental role in the dynamic responses of electron systems and form the basis of research into optical metamaterials 1 , 2 , 3 . Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour 4 , 5 , 6 , 7 that enables new tunable plasmonic metamaterials 8 , 9 , 10 and, potentially, optoelectronic applications in the terahertz frequency range 8 , 9 , 11 , 12 . Here we explore plasmon excitations in engineered graphene micro-ribbon arrays. We demonstrate that graphene plasmon resonances can be tuned over a broad terahertz frequency range by changing micro-ribbon width and in situ electrostatic doping. The ribbon width and carrier doping dependences of graphene plasmon frequency demonstrate power-law behaviour characteristic of two-dimensional massless Dirac electrons 4 , 5 , 6 . The plasmon resonances have remarkably large oscillator strengths, resulting in prominent room-temperature optical absorption peaks. In comparison, plasmon absorption in a conventional two-dimensional electron gas was observed only at 4.2 K (refs 13 , 14 ). The results represent a first look at light–plasmon coupling in graphene and point to potential graphene-based terahertz metamaterials.