Optical conductivity and the correlation strength of high temperature copper-oxide superconductors

TL;DR

This paper challenges the traditional view that high-temperature cuprate superconductors are Mott insulators with strong electron-electron repulsion, suggesting instead that antiferromagnetism plays a crucial role in their insulating and superconducting properties.

Contribution

It provides a comparative analysis of optical conductivity and theoretical models, revealing that cuprates are less strongly correlated than previously thought and emphasizing the importance of antiferromagnetism.

Findings

Correlation strength in cuprates is weaker than believed

Cuprates should not be classified as Mott insulators

Antiferromagnetism is key to insulating and superconducting states

Abstract

High temperature copper-oxide-based superconductivity is obtained by adding carriers to insulating "parent compounds". It is widely believed the parent compounds are "Mott" insulators, in which the lack of conduction arises from anomalously strong electron-electron repulsion, and that the unusual properties of Mott insulators are responsible for high temperature superconductivity. This paper presents a comparison of optical conductivity measurements and theoretical calculations which challenges this belief. The analysis indicates that the correlation strength in the cuprates is not as strong as previously believed, that the materials are not properly regarded as Mott insulators, that antiferromagnetism is essential to obtain the insulating state and, by implication, that antiferromagnetism is essential to the properties of the doped metallic and superconducting state as well.