Antiferromagnetic exchange and spin-fluctuation pairing in cuprate superconductors

TL;DR

This paper develops a microscopic theory for high-temperature superconductivity in cuprates, highlighting the roles of antiferromagnetic exchange and spin fluctuations in pairing mechanisms.

Contribution

It introduces a new theoretical framework based on the $p$-$d$ Hubbard model and Dyson equations, elucidating the pairing interactions and symmetry in cuprate superconductors.

Findings

High Tc is proportional to the Fermi energy due to antiferromagnetic exchange.

Numerical solutions confirm d-wave gap symmetry.

The model explains doping dependence, isotope effects, and pressure influence on Tc.

Abstract

A microscopic theory of superconductivity is formulated within an effective $p$-$d$ Hubbard model for a CuO2 plane. By applying the Mori-type projection technique, the Dyson equation is derived for the Green functions in terms of Hubbard operators. The antiferromagnetic exchange caused by interband hopping results in pairing of all carries in the conduction subband and high Tc proportional to the Fermi energy. Kinematic interaction in intraband hopping is responsible for the conventional spin-fluctuation pairing. Numerical solution of the gap equation proves the d-wave gap symmetry and defines Tc doping dependence. Oxygen isotope shift and pressure dependence of Tc are also discussed.