Saturation of the Magnetic Response of Split-Ring Resonators at Optical Frequencies

Abstract

We investigate numerically the limits of the resonant magnetic response with a negative effective permeability mu(eff) for single-ring multicut split-ring resonator (SRR) designs up to optical frequencies. We find the breakdown of linear scaling due to the free electron kinetic energy for frequencies above approximately 100 THz. Above the linear scaling regime, the resonance frequency saturates, while the amplitude of the resonant permeability decreases, ultimately ceasing to reach negative value. The highest resonance frequency at which mu(eff) < 0 increases with the number of cuts in the SRR. A LC circuit model provides explanation of the numerical data.

Metamaterials: a new frontier of science and technology

“…Furthermore, the amplitude of the resonant permeability from SRRs decreases and ultimately ceases to reach a negative value in the visible region. 19 These challenges impelled researchers to seek alternative designs other than the combination of metallic wires and SRRs. The most successful optical NIMs so far are the fishnet structure, [20][21][22] which consists of two layers of metal meshes separated by a dielectric spacer layer ( Fig.…”

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“…4 show a linear relation between the NRI region and the scaling factor, the linearity must break down for frequencies above 100 THz due to the free electron kinetic energy. 21,32,33 This is also forewarned by the transmission of the FH at resonance, which becomes lower when the NRI region shifts from the GHz to the THz range. Higher frequencies are more challenging not only because of dissipation owing to the increased optical losses, but also because the scaled-down geometrical parameters may challenge state-ofthe-art nanofabrication technologies.…”

An optical cloak made of dielectrics

“…Such stringent requirements are normally accompanied by strong dispersion, resulting in a cloak that only works in a narrow frequency range. Additionally, the strong magnetic response obtained in microwave metamaterials [5][6][7]9], where metal is close to being perfect, cannot be sustained at optical frequencies due to the higher loss and the kinetic inductance of the electrons, prohibiting a simple scaling to optical frequencies [10][11][12].…”