Superconductivity in a Hubbard-Froehlich Model and in cuprates

TL;DR

This study demonstrates that a weak long-range electron-phonon interaction can induce robust d-wave superconductivity in strongly correlated systems, suggesting a combined electron-electron and electron-phonon mechanism for high-temperature superconductivity.

Contribution

It shows that a weak long-range electron-phonon interaction induces d-wave superconductivity in doped Mott insulators, even with infinite Coulomb repulsion, highlighting a combined mechanism.

Findings

Superconductivity persists at infinite Coulomb repulsion.

Long-range electron-phonon interaction enhances superconducting condensation energy.

Superconductivity is robust against trial function variations.

Abstract

Using the variational Monte-Carlo method we find that a relatively weak long-range electron-phonon interaction induces a d-wave superconducting state of doped Mott-Hubbard insulators and/or strongly-correlated metals with a condensation energy significantly larger than can be obtained with Coulomb repulsion only. Moreover, the superconductivity is shown to exist for infinite on-site Coulomb repulsion, removing the requirement for additional mechanisms such as spin fluctuations to mediate d-wave superconductivity. We argue that the superconducting state is robust with respect to a more intricate choice of the trial function and that the true origin of high-temperature superconductivity lies in a proper combination of strong electron-electron correlations with poorly screened Froehlich electron-phonon interaction.