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.