Decay of plasmonic waves in Josephson junction chains

TL;DR

This paper investigates how plasma waves in Josephson junction chains decay due to quantum phase slips and nonlinear interactions, revealing a frequency-dependent relaxation behavior consistent with recent experiments.

Contribution

It provides a theoretical analysis of plasma wave damping mechanisms in Josephson junction chains, including the effects of quantum phase slips and nonlinearity, with predictions matching experimental observations.

Findings

Relaxation rate from nonlinearity scales as ω^4.

Quantum phase slip contribution follows a non-universal power law.

Quality factor ωτ exhibits non-monotonic frequency dependence.

Abstract

We study the damping of plasma waves in linear Josephson junction chains as well as in two capacitively coupled chains. In the parameter regime where the ground capacitance can be neglected, the theory of the antisymmetric mode in the double chain can be mapped onto the theory of a single chain. We consider two sources of relaxation: the scattering from quantum phase slips (QPS) and the interaction among plasmons related to the nonlinearity of the Josephson potential. The contribution to the relaxation rate $1/\tau$ from the nonlinearity scales with the fourth power of frequency $\omega$, while the phase-slip contribution behaves as a power law with a non-universal exponent. In the parameter regime where the charging energy related to the junction capacitance is much smaller than the Josephson energy, the amplitude of QPS is strongly suppressed. This makes the relaxation mechanism related to QPS efficient only at very low frequencies. As a result, for chains that are in the infrared limit on the insulating side of the superconductor-insulator transition, the quality factor $\omega\tau$ shows a strongly non-monotonic dependence on frequency, as was observed in a recent experiment.