Electrical control of optical plasmon resonance with graphene

Surface plasmon has the unique capability to concentrate light into subwavelength volume.(1-5) Active plasmon devices using electrostatic gating can enable flexible control of the plasmon excitations,(6) which has been demonstrated recently in terahertz plasmonic structures.(7-9) Controlling plasmon resonance at optical frequencies, however, remains a significant challenge because gate-induced free electrons have very weak responses at optical frequencies.(10) Here we achieve efficient control of near-infrared plasmon resonance in a hybrid graphene-gold nanorod system. Exploiting the uniquely strong(11, 12) and gate-tunable optical transitions(13, 14) of graphene, we are able to significantly modulate both the resonance frequency and quality factor of gold nanorod plasmon. Our analysis shows that the plasmon-graphene coupling is remarkably strong: even a single electron in graphene at the plasmonic hotspot could have an observable effect on plasmon scattering intensity. Such hybrid graphene-nanometallic structure provides a powerful way for electrical control of plasmon resonances at optical frequencies and could enable novel plasmonic sensing down to single charge transfer events.