Abstract
We investigate a novel implementation of hyperbolic metamaterial (HM) at far-infrared frequencies composed of stacked graphene sheets separated by thin dielectric layers. Using the surface conductivity model of graphene, we derive the homogenization formula for the multilayer structure by treating graphene sheets as lumped layers with complex admittances. Homogenization results and limits are investigated by comparison with a transfer matrix formulation for the HM constituent layers. We show that infrared iso-frequency wavevector dispersion characteristics of the proposed HM can be tuned by varying the chemical potential of the graphene sheets via electrostatic biasing. Accordingly, reflection and transmission properties for a film made of graphene-dielectric multilayer are tunable at terahertz frequencies, and we investigate the limits in using the homogenized model compared to the more accurate transfer matrix model. We also propose to use graphene-based HM as a super absorber for near-fields generated at its surface. The power emitted by a dipole near the surface of a graphene-based HM is increased dramatically (up to 5 × 10(2) at 2 THz), furthermore we show that most of the scattered power is directed into the HM. The validity and limits of the homogenized HM model are assessed also for near-fields and show that in certain conditions it overestimates the dipole radiated power into the HM.
Highlights
A stack of graphene sheets, separated by subwavelength dielectric spacers, can be regarded as a composite material with uniaxial electric properties under certain conditions
We have investigated a novel design of hyperbolic metamaterial (HM) for far-infrared frequencies based on graphene layers
The multilayer structure has been analyzed using effective medium approximation (EMA) which, based on a permittivity homogenization model, predicts the HM features at far-infrared frequencies
Summary
A stack of graphene sheets, separated by subwavelength dielectric spacers, can be regarded as a composite material with uniaxial electric properties under certain conditions. We show that stacking graphene sheets can be utilized for designing tunable HMs in a wide frequency spectrum ranging from millimeter-waves up to tens of terahertz frequencies, encompassing the whole far-infrared band. We show that most of the power is directed into the HM, offering a viable route for wide band and wide incidence-angle super absorption interfaces at far-infrared frequencies, as previously discussed in [3,9,13,42] for optical frequencies We show that this large enhancement of power emission is associated to the wide spatial spectrum being able to propagate inside the HM, that would be otherwise evanescent in free space
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