Abstract-Resonant absorption of terahertz waves in layered superconductors: Wood’s anomalies and anomalous dispersion

M. V. Mazanov, S. S. Apostolov, Z. A. Maizelis, N. M. Makarov, A. A. Shmat’ko, and V. A. Yampol’skii

https://journals.aps.org/prb/accepted/05078O5aTe81234941680a13a254c24e4aa661d81

We study theoretically the resonant absorption of THz electromagnetic waves of TM polarization in a slab of layered superconductor enclosed within twofold dielectric layers. Using the transfer-matrix method and assuming weak dissipation of waves in the sample, we analyze the absorption for both symmetric and antisymmetric bilateral incident radiation. The excitation of electromagnetic waves localized on the layered superconductor gives rise to the resonant absorption, phenomenon known as Wood’s anomaly, providing for suppression of the specular wave-reflection. This phenomenon is essentially modified in the layered superconductors as compared with usual conductors. The dispersion curves of localized modes are nonmonotonic, thus resulting in the specific dependence of the absorptance $A$ on the incidence angle $\theta$. We reveal the conditions for emergence of the resonant absorption and derive the asymptotic expressions for the resonant absorptance. A specific non-Lorentzian line shape of $A\left(\theta \right)$ dependence, like twin resonant peaks or merged single broad peak, appears when the wave frequency $\omega$ is tuned close to the top point on the dispersion curve $\omega \left(\theta \right)$. Experimental observation of such resonant line shapes can serve as a verification of the existence of localized waves with nonmonotonic dispersion in the layered superconductors.

Abstract-Anomalous dispersion of oblique terahertz waves localized in the plate of a layered superconductor

Low Temperature Physics

S. S. Apostolov,  Z. A. Maizelis,  D. V. Shimkiv,  A. A. Shmat’ko, V. A. Yampol’ski

The geometry of the problem: propagating at an angle θ to the z-axis (crystallographic axis c) in a plate of layered superconductor with thickness L, surrounded by a dielectric material, is the localized eigenmode with the wave vector k|| = (ky, kz) along the surface of the plate.

https://aip.scitation.org/doi/abs/10.1063/1.5116536

A theoretical study of localized waves propagating along a plate with finite thickness, made out of a layered superconductor with layers perpendicular to the surface of the plate. Due to the strong anisotropy of the layered superconductor, the electromagnetic field of the mode is a superposition of the ordinary and extraordinary waves that, in general, cannot be separated from each other. The dispersion law for an arbitrary direction of the propagation of such localized modes with respect to the layers is derived. It is shown that the dispersion curves may increase in both a monotonic and non-monotonic manner, i.e. they contain regions with anomalous dispersion. The frequencies at which the anomalous dispersion may be observed are determined as a function of the propagation angle. The dependence of the frequency on both the modulus of the longitudinal wave vector and its projections is analyzed. The results obtained may be of significant importance to practical applications in terahertz-range electronics.

Abstract-Excitation of terahertz modes localized on a layered superconductor: Anomalous dispersion and resonant transmission

S. S. Apostolov, N. M. Makarov, and V. A. Yampol’skii

https://journals.aps.org/prb/accepted/2c072O3fYab17830619e03387eefa4970c66e5010

We study theoretically the optic transmission through a slab of layered superconductor separated from two dielectric leads by spatial gaps. Basing on the transfer matrix formalism along with the Josephson plasma electrodynamic approach, we derive analytic expressions for the transmittance and identify the conditions for the perfect transmission. The special interest of the study is focused on the resonant transmission, which occurs when the wave does not propagate in the spatial gaps. Far from the resonance, the transmittance is exponentially small due to the total internal reflection from the lead-gap interface. However, the excitation of electromagnetic modes localized on the layered superconductor gives rise to a remarkable resonant enhancement of the transmission. Moreover, this phenomenon is significantly modified for the layered superconductors in comparison with usual dielectrics or conductors. The dispersion curves for the modes localized on the layered superconductor are proved to be non-monotonic, thus resulting in the specific dependence of the transmittance T on the incidence angle \theta. In particular, we predict the onset of two resonant peaks in the T(\theta) dependence and their subsequent merge into the broadened single peak with increasing the wave frequency. Our analytical results are demonstrated by numerical data.

Abstract-Transmission of terahertz waves through layered superconductors controlled by a dc magnetic field

S. S. Apostolov, Z. A. Maizelis, N. M. Makarov, F. Pérez-Rodríguez, T. N. Rokhmanova, and V. A. Yampol'skii

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.024513

The transmission of THz electromagnetic waves via a slab of layered superconductor in the presence of dc magnetic field H0 is theoretically studied. We demonstrate that the external dc field turns the layered superconductor into nonuniform medium with spatially and frequency-dependent dielectric permittivity. Even a relatively weak dc magnetic field, when the superconductor is in the Meissner state, significantly affects the transmittance of the layered superconductor. Moreover, the proper choice of H0 can provide the perfect transparency of the slab. In addition, the dc magnetic field changes the dependence of the transmittance on the slab thickness, the frequency, and the incident angle of the wave. Thus, it can serve as an effective tool to control the transmissivity of layered superconductors.

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Abstract-Transmission of terahertz waves through layered superconductors controlled by a dc magnetic field

S. S. Apostolov, Z. A. Maizelis, N. M. Makarov, F. Pérez-Rodríguez, T. N. Rokhmanova, and V. A. Yampol’skii


http://journals.aps.org/prb/accepted/0407bO77Z9c1fa2016e682b515aebb6c2da83a754

The transmission of THz electromagnetic waves via a slab of layered superconductor in the presence of DC magnetic field H0 is theoretically studied. We demonstrate that the external DC field turns the layered superconductor into non-uniform medium with spatially and frequency dependent dielectric permittivity. Even relatively weak DC magnetic field, when the superconductor is in the Meissner state, significantly affects the transmittance of the layered superconductor. Moreover, the proper choice of H0 can provide the perfect transparency of the slab. In addition, the DC magnetic field changes the dependence of the transmittance on the slab thickness, the frequency, and the incident angle of the wave. Thus, it can serve as an effective tool to control the transmissivity of layered superconductors.