Superfluid density of high-Tc cuprate systems: implication on condensation mechanisms, heterogeneity and phase diagram

TL;DR

This study uses muon spin relaxation to explore the superfluid density in high-Tc cuprates, revealing universal correlations, phase separation, and implications for condensation mechanisms, leading to a new phase diagram distinguishing pair formation and phase fluctuations.

Contribution

It provides new insights into heterogeneity, phase separation, and the condensation process in high-Tc cuprates, proposing a revised phase diagram based on these findings.

Findings

Universal correlation between Tc and superfluid density in cuprates.

Evidence of microscopic phase separation in strongly perturbed samples.

Proposal of a new phase diagram emphasizing pair formation and phase fluctuations.

Abstract

Extensive muon spin relaxation measurements have been performed to determine the magnetic field penetration depth in high-Tc cuprate superconductors with simple hole doping, Zn-doping, overdoping, and formation of static SDW nano islands. System dependence of $n_{s}/m^{*}$ (superconducting carrier density / effective mass) reveals universal correlations between Tc and $n_{s}/m^{*}$ in all these cases with / without perturbation. Evidence for spontaneous and microscopic phase separation was obtained in the cases with strong perturbation, i.e., Zn-doping. overdoping and SDW nano-islands. The length scale of this heterogeneity is shown to be comparable to the in-plance coherence length. We discuss implications of these results on condensation mechanisms of HTSC systems, resorting to an analogy with He films, on regular and porous media, reminding essential features of Bose-Einstein, BCS and Kosterlitz-Thouless condensation/transition in 2-d and 3-d systems, and comparing models of BE-BCS crossover and phase fluctuations. We propose a new phase diagram for HTSC systems based on distinction between pair formation and superconducting phase fluctuations in the pseudogap region and spontaneous phase separation in the overdoped region. We also remind anomaly in BEDT and A3C60 systems similar to that in overdoped cuprates, seen in the evolution from superconducting to metallic ground state.