Hybrid Metal-Graphene Plasmons for Tunable Terahertz Technology

Abstract

Among its many outstanding properties, graphene supports terahertz surface plasma wavessub-wavelength charge density oscillations connected with electromagnetic fields that are tightly localized near the surface [1,2]. When these waves are confined to finite-sized graphene, plasmon resonances emerge that are characterized by alternating charge accumulation at the opposing edges of the graphene. The resonant frequency of such a structure depends on both the size and the surface charge density, and can be electrically tuned throughout the terahertz range by applying a gate voltage [3,4]. The promise of tunable graphene THz plasmonics has yet to be fulfilled, however, because most proposed optoelectronic devices including detectors, filters, and modulators [5-10] desire near total modulation of the absorption or transmission, and require electrical contacts to the graphene -constraints that are difficult to meet using existing plasmonic structures. We report here a new class of plasmon resonance that occurs in a hybrid graphene-metal structure.The sub-wavelength metal contacts form a capacitive grid for accumulating charge, while the narrow interleaved graphene channels, to first order, serves as a tunable inductive medium, thereby forming a structure that is resonantly-matched to an incident terahertz wave. We experimentally demonstrate resonant absorption near the theoretical maximum in readily-available, large-area graphene, ideal for THz detectors and tunable absorbers. We further predict that the use of high mobility graphene will allow resonant THz transmission near 100%, realizing a tunable THz filter or modulator. The structure is strongly coupled to incident THz radiation, and solves a fundamental problem of how to incorporate a tunable plasmonic channel into a device with electrical contacts.

A Novel Method for PIT Effects Based on Plasmonic Decoupling

“…Gu et al found extremely confined THz SPPs in graphene-metal structures. [17] A tunable THz technology based on hybrid metal-graphene plasmons [18] has been experimentally demonstrated. Thongrattanasiri et al have designed periodically patterned graphene on a dielectric film on top of a thick metal for complete THz optical absorption.…”