Structural Chemistry, Spin Order, and the Distinction Between the Cuprate and Pnictide High-Temperature Superconductors

TL;DR

This paper explores how structural chemistry and spin order influence high-temperature superconductivity in cuprates and pnictides, highlighting differences in pairing symmetry and the role of fluorine in enhancing Tc.

Contribution

It presents a unified view of the roles of local structure and spin order in determining superconducting pairing symmetry and proposes methods to enhance Tc through fluorination.

Findings

Cuprates favor d-wave singlet pairing due to large on-site repulsion.

Pnictides favor s-wave singlet pairing, with less on-site repulsion.

Fluorine doping can significantly raise Tc in both cuprates and pnictides.

Abstract

In the cuprate and iron-pnictide systems, valence changes induce high-temperature superconductivity while the local structural chemistry and local spin order both independently generate the attractive interactions responsible for the high transition temperature. We argue that together they favor d-wave singlet superconductivity in the cuprates but s-wave singlet in the pnictides. This difference arises from the existence of a large on-site repulsion between carriers in the cuprates largely absent in the pnictides. Fluorine is responsible for raising Tc significantly in some pnictides and in the cuprates to 155K-168K, the highest achieved at ambient pressure. We propose an experimental procedure for finding and fabricating the fluorinated cuprate phase having that exceptional property.