Metamaterials are artificially created composite periodic structures with a unit cell much smaller than the targeted wavelength of the radiation. These materials may exhibit electromagnetic properties not found in nature. It appear that by using a suitable combination of composite constituents it is possible to conceive for example an “invisibility cloak” or plates with a negative refractive index allowing one to overcome the diffraction limit in the optical imaging. However, these properties can be used in a narrow spectral range only restricted by the width of very sharp magnetic resonances (in permeability). For this reason we proposed and experimentally realized a metamaterial with a tunable range of negative effective permeability in the terahertz spectral range (0.2 – 0.36 THz) [
H. Němec et al., Phys. Rev. B 79, 241108 (2009)].
This structure consists of an array of nonmagnetic rods made of an incipient ferroelectric SrTiO
3 which shows a high tunable permittivity. The magnetic response and its tuning are achieved by a temperature control of the permittivity of SrTiO
3, which defines the resonant confinement of the electromagnetic field within the rods (so called Mie resonances). The spectral positions
of resonances depend on the geometrical parameters of the rods and on their tunable permittivity. The electromagnetic coupling between the adjacent rods is negligible. With a suitable aspect ratio of the rods, a broadband magnetic response can be obtained [
R. Yahiaoui et al., Opt. Lett. 34, 3451 (2009)].
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Fig. 1: (a) Scanning electron microscope image of the metamaterial. (b) Transmittance spectra of the metamaterial for various temperatures. The dip corresponds to the lowest Mie resonance which is associated with strong effective magnetic behavior. (c) Effective magnetic permeability (Re μ and Im μ) of the metamaterial.
