Electronic correlations, electron-phonon interaction, and isotope effect in high-Tc cuprates

TL;DR

This paper investigates how electron correlations and phonons influence superconductivity in high-Tc cuprates, showing phonons enhance Tc and isotope effects vary with doping, using a large-N expansion of a generalized t-J model.

Contribution

It introduces a large-N expansion approach to solve the superconducting gap equation in a t-J model with phonons, revealing phonon contributions to Tc and isotope effects.

Findings

Phonons positively contribute to Tc in high-Tc cuprates.

The isotope coefficient is small at optimal doping and increases with doping.

The model reproduces the doping dependence of isotope effects observed experimentally.

Abstract

Using a large-N expansion we present and solve the linearized equation for the superconducting gap for a generalized t-J model which also contains phonons within a Holstein model. The leading Tc has d-wave symmetry with phonons giving a positive contribution to Tc. The corresponding isotope coefficient is very small at optimal doping and increases towards the classical value 1/2 with increasing dopings similar as in many cuprates.