We theoretically study the infrared reflectivity and transmissivity of a high-temperature layered superconductor slab. Both infrared spectra exhibit very narrow Fabry-Perot resonances associated with the quantization of the wave vector of the TM electromagnetic modes. The resonances are observed in a pass band where the refractive index of the layered superconductor is negative. The pass band of negative dispersion is above the Josephson plasma frequency which appears in the expression for the effective permittivity component, corresponding to the direction perpendicular to the layers. It was found that the Fabry-Perot resonances undergo a blue shift as the slab thickness or the angle of incidence are increased. Moreover, the quantized electromagnetic modes turn out to be quasi-longitudinal because of the strong anisotropy of the infrared dielectric response of the layered superconductor.
The diffraction of terahertz (THz) electromagnetic waves by a grating, composed of alternating layered high-temperature-superconductor bars and dielectric bars, is theoretically studied. The formalism of the finite Fourier transform is applied for calculating the relative intensities of the diffracted THz waves. Assuming that the superconducting layers and the electric field of the incident electromagnetic wave are parallel to the axes of the grating bars, it is found that the intensity T0 of the zero-order diffracted waves into the substrate vanishes at low frequencies even at very small superconductor filling fractions. However, at frequencies just below the lowest cutoff frequency, the transmissivity T0 turns out to be considerably enhanced and its relatively large value is maintained at higher frequencies.
We theoretically study the effect of the spatial dispersion on the optical response of a layered hightemperature superconductor slab. The nonlocality of the inherently-anisotropic layered superconductor comes from the wave vector dependence of its average permittivity tensor, and leads to the generation of additional electromagnetic modes just above the characteristic Josephson plasma frequency, that is in the terahertz range.We calculate p-polarization optical spectra for a Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) superconductor slab, which show very narrow resonances associated with the quantization of the wave vectors of both long-wavelength electromagnetic modes, having negative dispersion, and short-wavelength additional (nonlocal) modes of positive dispersion. The dependence of the frequency position and shape of the resonances on the nonlocality parameter, the slab thickness, and the components of the quasiparticle conductivity is analyzed. We have found that the quantized longwavelength modes of negative dispersion, which can only be observed at relatively-large slab thicknesses, give rise to prominent resonances in the p-polarization reflectivity spectrum. On the other hand, the resonances associated with quantized additional short-wavelength electromagnetic modes are weak, but they can be clearly observed when the superconductor slab thickness is smaller than the smallest magnetic-field penetration depth.
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