Superconductivity in strongly correlated systems for local repulsive interactions

TL;DR

This paper investigates superconductivity in a 2D Hubbard model with local repulsive interactions, revealing a kinetic-energy-mediated superconducting state and phase diagram features at zero and finite temperatures.

Contribution

It introduces a Green's function approach within Hubbard-I approximation to analyze superconductivity in strongly correlated systems with repulsive interactions.

Findings

Superconducting ground state exists in the repulsive Hubbard model.

A minimum repulsion strength $U_{min}$ is needed for pairing.

Critical temperature $T_c$ saturates at strong interactions, similar to Bose-Einstein condensation.

Abstract

The understanding of the mechanisms responsible for superconductivity in strongly correlated systems is an interesting and important subject in condensed matter physics. Several theoretical proposals were considered for these systems. The Coulomb interaction between electrons allow a new approach to study this problem. In this paper, we use a usual Hubbard model with a local repulsive interaction to describe a 2D system. The system of equations are solved using the Green's functions method, within a Hubbard-I mean field approximation, which allows to treat the strong interaction limit. We consider both cases of attractive and repulsive interactions and obtain the zero temperature phase diagram of the model. Our results show, in the repulsive case, the existence of a superconducting ground state mediated by the kinetic electronic energy and described by a non-local order parameter. A minimum value of the repulsive interaction $U_{min}$ is required to create a pairing state. At finite temperatures, for strong interactions, the critical temperature $T_c$ shows a saturation similar to the Bose-Einstein condensation observed for strong attractive interactions.