Evidence that cuprate superconductors form an array of nanoscopic Josephson junctions

TL;DR

This paper proposes that cuprate superconductors consist of nanoscopic Josephson junctions formed by charge density wave domains, explaining key phenomena like the pseudogap and superfluid density.

Contribution

It introduces a model where charge domains act as granular superconductors coupled via Josephson junctions, providing new insights into cuprate superconductivity mechanisms.

Findings

Charge density waves form in CuO planes creating energy wells.

Charge oscillations induce hole-hole attraction proportional to barrier height.

The model reproduces superfluid density temperature dependence and proximity effects.

Abstract

Recent measurements of charge instabilities in overdoped compounds rekindled the proposal that cuprates become superconductors by long-range order through Josephson coupling between nanoscopic charge domains. We use the theory of phase-ordering dynamics to show that incommensurate charge density waves (CDWs) are formed in the CuO planes by a series of free-energy wells separated by steep barriers. Charge oscillations in these domains give rise to a net hole-hole attraction proportional to the height of these barriers. Concomitantly, the self-consistent calculations yield localized superconducting amplitudes in the CDWdomains characterizing a granular superconductor. We show that a transition by long-range phase order promoted by Josephson coupling elucidates many well-known features of cuprates like the high magnetic penetration depth anisotropy and the origin of the pseudogap, among others. Furthermore, the average Josephson energy reproduces closely the planar superfluid density temperature dependence of La-based films and the superconducting giant proximity effects of cuprates, a 20-year-old open problem.