Highly Correlated Electron State and High-Temperature Superconductivity in Iron Pnictides

TL;DR

This paper confirms and refines a model of high-temperature superconductivity based on highly correlated electron states and Coulomb interactions, applying it to iron pnictides and relating it to chemical bonding and quantum electron crystals.

Contribution

It extends a previously proposed model of superconductivity to iron pnictides, emphasizing the role of highly correlated electrons and Coulomb interactions in these materials.

Findings

Superconductivity is linked to a transition of FeAs layers into a highly correlated electron state.

Formation of two-dimensional electron pair crystals with quantized energy levels is observed.

Superconductivity involves a two-dimensional Wigner crystal of bosonic electron pairs.

Abstract

It is shown that the qualitative model of the high-temperature superconductivity suggested earlier for cuprates and doped picene and based on the idea that the valence electron state depends on the character of the chemical bonds they form and on the Coulomb interaction between the electrons is not only confirmed by the experimental data on iron pnictides but is also improved. From the chemical point of view, the high-temperature superconductivity is associated with additional $\pi$ bonding along chains of covalently bonded ions via a delocalized $\pi$ orbital, just like in cuprates. From the physical point of view, as the data on iron pnictides show, the superconductivity is associated with a FeAs layer transition into the state similar to a macroscopic quantum system characterized by a highly correlated electron state, formation of two-dimensional crystals of electron pairs with quantized energy levels, and a strong Coulomb interaction between these crystals. Superconductivity in such a system is accomplished by a two-dimensional Wigner crystal consisting of one-dimensional Wigner crystals formed by bosons, i.e., singlet electron pairs that are in the same quasi-one-dimensional state extending along the ion chain, which corresponds to a delocalized $\pi$ orbital in chemistry. The model applicability to three different classes of materials (cuprates, picene, iron pnictides) indicates that it can prove useful for development of the theory of superconductivity taking into consideraion the highly correlated state of valence electrons and strong Coulomb interactions between the electrons.