The magnetic field induced phase separation in a model of a superconductor with local electron pairing

TL;DR

This paper investigates how an external magnetic field can induce phase separation in a model of a superconductor with local electron pairing, revealing complex phase behavior and transitions.

Contribution

It introduces a study of magnetic field effects on phase separation in an extended Hubbard model with pair hopping, using a variational approach and mean-field approximation.

Findings

Magnetic field can induce phase separation between superconducting and non-ordered states.

The phase diagram includes homogeneous and phase-separated states depending on parameters.

Field-induced phase separation occurs at higher fields than the superconducting phase.

Abstract

We have studied the extended Hubbard model with pair hopping in the atomic limit for arbitrary electron density and chemical potential and focus on paramagnetic effects of the external magnetic field. The Hamiltonian considered consists of (i) the effective on-site interaction U and (ii) the intersite charge exchange interactions I, determining the hopping of electron pairs between nearest-neighbour sites. The phase diagrams and thermodynamic properties of this model have been determined within the variational approach (VA), which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. Our investigation of the general case shows that the system can exhibit not only the homogeneous phases: superconducting (SS) and nonordered (NO), but also the phase separated states (PS: SS-NO). Depending on the values of interaction parameters, the PS state can occur in higher fields than the SS phase (field-induced PS). Some ground state results beyond the VA are also presented.