Mixed phase and bound states in the phase diagram of the extended Hubbard model

TL;DR

This paper explores the phase diagram of the extended Hubbard model, revealing the stabilization of mixed states with multiple order parameters and analyzing how two-electron bound states influence the competition between superconducting and normal phases.

Contribution

It demonstrates the possibility of mixed phase stabilization with three nonzero order parameters and applies an exact two-electron bound state solution to refine the phase diagram.

Findings

Mixed states with charge density waves, superconductivity, and eta-superconductivity can be stabilized.

Two-electron bound states can suppress s-wave superconductivity, favoring the normal state.

Exact solutions provide insights into phase competition in the model.

Abstract

The paper examines part of the ground state diagram of the extended Hubbard model, with the on-site attraction U<0 and intersite repulsion W>0 in the presence of charge density waves, superconducting and $\eta$-superconducting order parameters. We show the possibility of the stabilization of the mixed state, with all three nonzero order parameters, in the model with nearest neighbor interactions. The other result of the paper is application of the exact solution of the Schrodinger equation for the two electron bound state, as an additional bound for the phase diagram of the model, resulting in the partial suppression of the superconducting state of the s-wave symmetry, in favor of the normal state phase.