Nature Mater.http://dx.doi.org/10.1038/nmat3433 (2012)

Credit: © 2012 NPG

Although graphene possesses gate-controlled electronic properties that make it possible to manipulate light, these effects are not strong enough for practical use. Now, by combining graphene and metamaterials, Seung Hoon Lee and co-workers from Korea and the USA have demonstrated a compact device that can perform efficient terahertz wave switching and modulation. The device is made from a thin and flexible polymeric substrate that features an array of meta-atoms, an atomically thin gated graphene layer and an array of metallic wire gate electrodes. The meta-atoms comprise a hexagonal metallic frame of asymmetric double split rings exhibiting a Fano-like resonance. By applying a gate voltage to one of the electrodes, graphene's Fermi level — and hence its carrier density — can be dynamically controlled with a corresponding change in conductivity. This alters the complex permittivity of the graphene layer and thus changes the transmission of terahertz waves through the metamaterial. The researchers obtained amplitude and phase modulations of up to 47% and 32.2°, respectively, despite the graphene layer being six orders of magnitude thinner than the wavelength of incident light. They attribute this substantial increase in modulation to the enhanced light–matter interaction in the graphene layer, which is due to the strong resonances of the metamaterial. The researchers also observed hysteresis-like behaviour in the terahertz wave transmission, indicating persistent photonic memory effects that could be useful for an electrically controllable photonic memory. Other possible applications include tunable or reconfigurable terahertz devices.