Superconducting phase diagrams of cuprates and pnictides as a key to the HTSC mechanism

TL;DR

This paper reviews experimental phase diagrams of cuprates and pnictides, proposing that localized trion complexes and their percolation explain key features of high-temperature superconductivity.

Contribution

It introduces a novel approach linking dopant-induced CT plaquettes and percolation to the superconducting phase diagrams of HTSC materials.

Findings

Dopant concentration ranges match superconducting domes.

Percolation of CT plaquettes correlates with superconductivity.

Biexciton complexes facilitate pairing mechanisms.

Abstract

This paper reviews experimental phase diagrams of cuprates and pnictides to demonstrate that specific features of the superconducting phase diagrams in bothHTSC families can be understood within the framework of the proposed approach,which assumes the formation, under heterovalent doping, of localized trion complexes consisting of a doped carrier and charge transfer (CT) excitons. The geometry of such cells containing CT excitons (CT plaquettes) in the basal plane of the crystal is determined by its crystal structure and the type of dopant, so that the dopant concentration range corresponding to the existence of a percolation cluster of CT plaquettes can be readily determined for each particular compound. These dopant concentration ranges coincide with good accuracy with the experimental ranges of superconducting domes in the phase diagrams of the HTSC compounds considered. The generation of free carriers and the mechanism of superconducting pairing in this pattern is related to biexciton complexes (Heitler-London centers) emerging in neighboring CT plaquettes.