Fluctuation broadening of plasma resonance line in the vortex liquid state of layered superconductors

TL;DR

This paper explains how density fluctuations of pancake vortices in layered superconductors cause broadening and asymmetry in the Josephson plasma resonance line, revealing universal behavior influenced by superconductor parameters and temperature.

Contribution

It introduces a mechanism linking vortex density fluctuations to JPR line broadening and asymmetry, providing a universal shape description based on superconductor parameters and temperature.

Findings

JPR line broadening is mainly due to random Josephson coupling from vortex density fluctuations.

The line shape is universal and determined by superconductor parameters and temperature.

Asymmetric line shape with high-frequency tail from mode mixing and low-frequency tail from localized modes.

Abstract

The Josephson plasma resonance (JPR) provides a sensitive probe of vortex states in layered superconductors. We demonstrate that in the case of weak damping in the liquid phase, broadening of the JPR line is caused mainly by random Josephson coupling arising from the density fluctuations of pancake vortices. In this case the JPR line has the universal shape, which is determined only by parameters of the superconductors and temperature. This mechanism gives a natural explanation for the experimentally observed asymmetric lineshape. The tail at high frequencies arises due to mixing of the propagating plasma modes by random Josephson coupling, while the tail at small frequencies is caused by the localized plasma modes originating from a rare fluctuation suppression of the Josephson coupling in large areas.