Phase separation of superconducting phases in the Penson-Kolb-Hubbard model

TL;DR

This study maps the phase diagrams of the Penson-Kolb-Hubbard model on a 2D lattice, revealing phase separation between different superconducting states and temperature-induced symmetry changes, with complex multicritical phenomena.

Contribution

It provides the first detailed phase diagrams including phase separation and symmetry transitions in the Penson-Kolb-Hubbard model at finite temperatures.

Findings

Phase separation occurs between s-wave and η-wave superconducting phases.

Temperature can induce a transition from η-wave to s-wave symmetry.

The phase diagrams exhibit multicritical points and bicritical behavior.

Abstract

In this paper we determine the phase diagrams (for $T=0$ as well as $T>0$) of the Penson-Kolb-Hubbard model for two dimensional square lattice within Hartree-Fock mean-field theory focusing on investigation of superconducting phases and possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with $s$-wave and $\eta$-wave symmetries), occurs in define range of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from $\eta$-wave into $s$-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points.