Josephson coupling in Lanthanum-based cuprates superlattices

TL;DR

This paper demonstrates Josephson-like transport in artificially engineered La-based cuprate superlattices, revealing phase dynamics and low Josephson coupling, which enhances understanding of high-temperature superconductivity in layered materials.

Contribution

It provides experimental evidence of Josephson phase dynamics in LaSrCuO-LaCuO superlattices, a novel artificial structure, and explores their superconducting properties and phase behavior.

Findings

Evidence of Josephson phase dynamics at low temperatures.

Low Josephson coupling and phase diffusion observed.

Superlattice tuning enriches high-temperature superconductor phase diagram.

Abstract

In most anisotropic compounds such as bismuth-based layered cuprate perovskites, the supercurrent across the blocking layer is of Josephson type, and a single crystal forms a natural stack of Josephson junctions. Here, we report on the evidence of Josephson-like transport in an artificial cuprate superlattice composed of 10 LaSrCuO-LaCuO repeats, creating a superlattice of junctions, where LCO is a superconducting Mott insulator and LSCO an overdoped metal, respectively. The superlattice has been designed with a long period d = L+W = 5.28 nm, with L and W the thickness of LCO and LSCO units, respectively, and is in the underdoped regime with an average doping level < {\delta} >= 0.11. Quantum-size effects and Rashba spin-orbit coupling are controlled by L/d = 0.75, with a quasi-2D superconducting transition temperature of 41 K and a c-axis coherence length of about 1.5 nm. Measurements at very low temperatures show evidence of Josephson phase dynamics consistent with very low Josephson coupling and a phase diffusion regime, thus explaining why Josephson coupling in LSCO superlattices has been so elusive. The tuning of LSCO superlattices in the Josephson regime enriches the phase diagram of HTS.