Transverse optical plasmons in layered superconductors

TL;DR

This paper explores the theoretical existence of transverse optical plasma modes in layered superconductors, aligning with experimental observations of plasma peaks in optical conductivity measurements.

Contribution

It introduces a model predicting transverse optical plasma modes in superlattices of Josephson coupled layers, extending understanding of plasma excitations in layered superconductors.

Findings

Model predicts transverse optical plasma modes in layered superconductors.

Quantitative agreement with experimental optical conductivity data.

Identifies conditions for the existence of these modes.

Abstract

We discuss the possible existance of transverse optical plasma modes in superlattices consisting of Josephson coupled superconducting layers. These modes appear as resonances in the current-current correlation function, as opposed to the usual plasmons which are poles in the density-density channel. We consider both bilayer superlattices, and single layer lattices with a spread of interlayer Josephson couplings. We show that our model is in quantitative agreement with the recent experimental observation by a number of groups of a peak at the Josephson plasma frequency in the optical conductivity of La$_{1.85}$Sr$_{0.15}$CuO$_4$