Surface and waveguide Josephson plasma waves in slabs of layered superconductors

We discuss the propagation of symmetric and antisymmetric Josephson plasma waves in a slab of layered superconductor clad between two identical dielectrics. We predict two branches of surface waves in the terahertz frequency range, one above and another below the Josephson plasma frequency. Apart from this, there exists a discrete set of waveguide modes with electromagnetic fields oscillating across the slab thickness and decaying exponentially away from the slab. We consider the excitation of the predicted waves by means of the attenuated-total-reflection method. It is shown that for a specific set of the parameters of the structure, the excitation of the waveguide modes is accompanied by the total suppression of specular reflection

Surface Josephson Plasma Waves in Layered Superconductors above the Plasma Frequency: Evidence for a Negative Index of Refraction

We predict a new branch of surface Josephson plasma waves (SJPWs) in layered superconductors for frequencies higher than the Josephson plasma frequency. In this frequency range, the permittivity tensor components along and transverse to the layers have different signs, which is usually associated with negative refraction. However, for these frequencies, the bulk Josephson plasma waves cannot be matched with the incident and reflected waves in the vacuum, and, instead of the negative-refractive properties, abnormal surface modes appear within the frequency band expected for bulk modes. We also discuss the excitation of high-frequency SJPWs by means of the attenuated-total-reflection method. DOI: 10.1103/PhysRevLett.104.187003 PACS numbers: 74.25.NÀ, 42.25.Bs, 74.25.Gz, 78.20.Ci High-T c layered cuprate superconductors are important candidates for negative-refractive-index (NRI) metamaterials (see, e.g., Experiments for the c-axis conductivity in layered superconductors prove the use of a model in which the superconducting CuO 2 layers are coupled by the intrinsic Josephson effect through the layers The Josephson current along the c-axis couples with the electromagnetic field inside the insulating dielectric layers, forming Josephson plasma waves (JPWs) (see the review [5] and references therein). Thus, the propagation of electromagnetic waves through the layers is favored by the layered structure. The study of these waves is very important because of their terahertz frequency range, which is still hardly reachable for electronic and optical devices. As in common plasma waves, JPWs propagate with frequencies above some threshold value (the Josephson plasma frequency ! J ). However, in the frequency range below ! J , the presence of the sample boundary can produce surface Josephson plasma waves (SJPWs) At frequencies ! higher than the Josephson plasma frequency ! J , the normal-to-the-layers components of both the group velocity and the Poynting vector of propagating JPWs have signs opposite to the sign of the normal component of the wave vector k s . This corresponds to a NRI. However, the condition ! > ! J is not sufficient for NRI. This NRI effect can be observed at the vacuumlayered superconductor boundary only in a relatively narrow frequency range, , where " is the interlayer dielectric constant. A similar limitation exists for any insulator-layeredsuperconductor boundary, if the dielectric constant " ext of the insulator is less than ". The above conditions follow from the dispersion relation for the JPWs and the natural limitation for the tangential component q (q ¼ k sin < k, k ¼ !=c) of the wave vector for a wave incident at an angle from the vacuum onto the layered superconductor. A simple analysis shows that the above inequality is compatible with the dispersion relation for JPWs only for frequencies ! J < ! < ! PRL 104, 187003 (2010