Phase Separation of Superconducting Phases in the Penson–Kolb–Hubbard Model

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 η-wave symmetries), occurs in define range of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points.

Critical behavior in one dimension: Unconventional pairing, phase separation, BEC-BCS crossover, and magnetic Lifshitz transition

“…In contrast to the fixed chemical potential case, if the number of particles is fixed and n = 1, the phase separated states are present on the diagrams. The occurrence of the phase separated states for fixed concentration (so-called macroscopic phase separation) is associated with the first order phase transitions occurring for fixed µ [8,81]. Due to the fact that the transition for fixed µ between the FFLO and BCS phases, the BCS and NO phases, and the η-FFLO and NO phases (in some ranges of the model parameters) are discontinuous, the corresponding phase separated states are present on the diagrams as a function of n. One can distinguish three different phase separation regions in the h − |n − 1| phase diagram: PS1the region of phase separation between BCS and FFLO phases as well as between the BCS and NO phases (for h above and below, respectively, the points indicated by the arrow in Fig.…”

Phase Transitions in Quasi-One-Dimensional System with Unconventional Superconductivity

“…Refs. [43][44][45][46] and references therein). If n changes discontinuously from n − to n + at the boundary line between two phases in the diagram for fixed µ, the phases can co-exist on the phase diagram as a function of n. The dependence of particle concentration n (precisely the value of |n − 1|) with changing the model parameters is shown in Fig.…”

Phase separations induced by a trapping potential in one-dimensional fermionic systems as a source of core-shell structures

“…In such a phase-separated state two domains with different particle concentrations n − and n + coexist (there can be also regions differing in the magnitude of the order parameter as well as thermodynamic phases). In this approach, because of neglecting the interface energy at the boundaries of the domains, such states can exist only in the thermodynamic limit (i.e., when N → ∞) [54][55][56][57][58] . In a finite system, the interface energy can lead to an occurrence of states with other textures [59][60][61][62][63] , besides the homogeneous states and the phase separated states discussed above.…”