Surface Josephson Plasma Waves in Layered Superconductors

We predict the existence of surface waves in layered superconductors in the THz frequency range, below the Josephson plasma frequency ${\omega }_J$. This wave propagates along the vacuum-superconductor interface and dampens in both transverse directions out of the surface (i.e., towards the superconductor and towards the vacuum). This is the first prediction of propagating surface waves in any superconductor. These predicted surface Josephson plasma waves are important for different phenomena, including the complete suppression of the specular reflection from a sample (Wood’s anomalies) and a huge enhancement of the wave absorption (which can be used as a THz detector).

Figure 1

Spectra of two branches “$\pm$” of the surface Josephson plasma waves for the parameters $\alpha =0.1$ and $\beta =1.4$, standard for Bi2212. The inset shows the geometry used.

Figure 2

(a) Schematic diagram showing the mechanism of excitation of the surface waves along the superconductor-vacuum interface. To zero-order approximation, with respect to the amplitude $\mu$ of the spatial modulations in a superconducting sample, an incident wave (shown as a solid red arrow) reflects as a specular wave (the straight dashed blue arrow), producing a damped wave (solid green wave) inside superconductors. To first order approximation, the very intense surface wave (dotted magenta wave) can be excited at a certain resonant angle between the incident wave and sample surface. (b) Absorption obtained using Eq. (18) for different effective dampings $\delta =\beta {\omega }_r\alpha {\Omega }^4(Q_{+}^2-{\Omega }^2{)}^{1/2}[2{\omega }_J(1-{\Omega }^2{)}^3{Q}_{+}\cos {\theta }_0{]}^{-1}$.