Enhancement of Tc in Oxide Superconductors: Double-Bridge Mechanism of High-Tc Superconductivity and Bose-Einstein Condensation of Cooper Pairs

TL;DR

This paper proposes a double-bridge mechanism involving ionic bonds and Cooper pair attraction to explain and potentially enhance the superconducting transition temperature (Tc) in oxide superconductors, aiming for room-temperature superconductivity.

Contribution

It introduces a novel double-bridge mechanism and a strong-coupling pairing model based on atom-bridge interactions, offering new strategies for increasing Tc in ionic oxide superconductors.

Findings

High Tc of 138K in Hg0.8Tl0.2Ba2Ca2Cu3O8.33 demonstrated.

Tc is inversely proportional to the effective mass of Cooper pairs.

Enhancing Cooper pair attraction and optimizing pair density can increase Tc.

Abstract

The cuprate Hg0.8Tl0.2Ba2Ca2Cu3O8.33 exhibits the highest superconducting transition temperature Tc of 138K. Achieving superconductivity at even higher temperatures, up to room temperature, represents the ultimate dream of humanity. As temperature increases, Cooper pairs formed through weak electron-phonon coupling will be disintegrated by the thermal motion of electrons, severely limiting the enhancement of Tc. It is imperative to explore new strong-coupling pairing pictures and establish novel condensation mechanism of Cooper pairs at higher temperature. Based on our recently proposed groundbreaking idea of electron e- (hole h+) pairing bridged by oxygen O (metal M) atoms, namely, the eV-scale ionic-bond-driven atom-bridge (bridge-I) e--O-e- (h+-M-h+) strong-coupling itinerant Cooper pairing formed at pseudogap temperature T*>Tc in ionic oxide superconductors, we further discover that there is an attractive interaction between two Cooper pairs induced by the bridge atom (bridge-II) located between them. It is this attraction mediated by the bridge-II atoms that promotes all the Cooper pairs within the CuO2 plane to hold together and enter the superconducting state at Tc finally. Moreover, according to the Bose-Einstein condensation theory, we find that Tc is inversely proportional to the effective mass m* of Cooper pairs, directly proportional to n2/3s (ns: the density of Cooper pairs), and linearly increases with the scattering length a<0 due to attraction between two Cooper pairs. Therefore, according to our double-bridge mechanism of high-Tc superconductivity, increasing the attraction between Cooper pair and bridge-II atom, ensuring that ns takes the optimal value, and minimizing the effective mass of the Cooper pairs are the main approaches to enhancing Tc of ionic-bonded superconductors, which opens up a new avenue with clear direction for designing higher Tc superconductors.