Explanation of the Phase Diagram of High-Temperature Superconductors in Terms of the Model of Negative-U Centers Superconductivity

TL;DR

This paper offers a unified qualitative explanation for the complex phase diagram of high-temperature superconductors using the negative-U centers model, linking various phases and transitions to electron interactions with these centers.

Contribution

It introduces a novel qualitative model explaining the phase diagram of HTSC through negative-U centers and their interactions with valence band electrons.

Findings

Four distinct regions in the phase diagram are explained by the model.

Transitions between phases are accounted for by negative-U center interactions.

The relative concentration of electrons in negative-U centers is key to HTSC properties.

Abstract

It is demonstrated qualitatively how a unified explanation of the wide variety of different regions in a typical phase diagram of HTSC can be given in terms of the model of negative-U centers superconductivity. Both the existence of four regions (pseudogap, superconducting, non Fermi-liquid and Fermi-liquid), in the phase diagram and all the transitions between these regions were explained by assuming that negative-U centers exist in HTSC and qualitatively taking into account their thermodynamic and direct quantum-mechanical interaction with ordinary electrons from the valence band. It is found that the principal parameter determining the properties of HTSC in the model of negative-U centers is the relative concentration of electrons belonging to negative-U centers. The negative-U centers naturally determine both the superconducting properties of HTSC systems and the entire phase diagram in the normal state.