Josephson effect as a measure of quantum fluctuations in the cuprates

TL;DR

This paper demonstrates that analyzing the Josephson effect can reveal quantum phase fluctuations in cuprate superconductors, suggesting proximity to an exotic phase with electron quadruplet condensation.

Contribution

It introduces a phenomenological model of quantum fluctuations between pairing symmetries in cuprates and applies it to interpret Josephson effect measurements.

Findings

Quantum fluctuations between d-wave and s-wave pairing are significant at low temperatures.

Cuprate parameters suggest proximity to an exotic superconductor phase with electron quadruplet condensation.

Analysis provides direct insight into phase fluctuations in high-temperature superconductors.

Abstract

Quantitative analysis of the Josephson effect is shown to provide direct information about phase fluctuations in the superconducting banks. Applying the analysis to the cuprates, substantial quantum fluctuations between d-wave and s-wave pairing are found at low temperatures. A phenomenological model of such fluctuations is introduced and solved in a self-consistent single-site approximation. The cuprate parameters are argued to lie close to an exotic superconductor phase with condensation of electron quadruplets.