Surface waves versus negative refractive index in layered superconductors

TL;DR

This paper predicts a new type of surface Josephson plasma waves in layered superconductors at frequencies above the plasma frequency, revealing unusual surface modes related to negative permittivity components.

Contribution

It introduces a novel branch of surface Josephson plasma waves occurring at high frequencies, differing from bulk modes and associated with negative permittivity tensor components.

Findings

Discovery of a new surface wave branch in layered superconductors.

Surface modes appear without negative refraction despite negative permittivity.

Potential excitation of these modes via attenuated-total-reflection method.

Abstract

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.