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 metamaterials1, 2, 3. Plasmons of two-dimensional massless electrons, as present in graphene, show unusual behaviour4, 5, 6, 7 that enables new tunable plasmonic metamaterials8, 9, 10 and, potentially, optoelectronic applications in the terahertz frequency range8, 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 electrons4, 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.
At a glance
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