Plasma Waves in Anisotropic Superconducting Films Below and Above the Plasma Frequency

TL;DR

This paper analyzes wave propagation in anisotropic superconducting films near and above the plasma frequency, revealing distinct dispersion relations and guided wave behaviors with potential experimental implications.

Contribution

It provides a theoretical analysis of plasma wave modes in anisotropic superconducting films, including dispersion relations below and above the plasma frequency, and describes guided wave behavior.

Findings

Below plasma frequency, dispersion relation follows ω ∝ √β and ω ∝ 1/√β.

Above plasma frequency, propagation is guided with dispersion ω ≈ ω_p √(1 + (β/β_0)^2).

Modes are confined and reflect within the superconducting film.

Abstract

We consider wave propagation inside an anisotropic superconducting film sandwiched between two semi-infinite non-conducting bounding dieletric media such that along the c-axis, perpendicular to the surfaces, there is a plasma frequency $\omega_p$ below the superconducting gap. Propagation is assumed to be parallel to the surfaces in the dielectric medium, where amplitudes decay exponentially.Below $\omega_p$, the amplitude also evanesces inside the film, and we retrieve the experimentally measured lower dispersion relation branch, $\omega \propto \sqrt{\beta}$, and the recently proposed higher frequency branch, $\omega \propto 1/\sqrt{\beta}$.Above $\omega_p$, propagation is of the guided wave type, i.e., a dispersive plane wave confined inside the film that reflects into the dielectric interfaces,and the modes are approximately described by $\omega \approx \omega_p \sqrt{ 1+ (\beta/\beta_0)^2}$, where $\beta_0$ is discussed here.