8 research outputs found
The effects of the next-nearest-neighbour density-density interaction in the atomic limit of the extended Hubbard model
We have studied the extended Hubbard model in the atomic limit. The
Hamiltonian analyzed consists of the effective on-site interaction U and the
intersite density-density interactions Wij (both: nearest-neighbour and
next-nearest-neighbour). The model can be considered as a simple effective
model of charge ordered insulators. The phase diagrams and thermodynamic
properties of this system have been determined within the variational approach,
which treats the on-site interaction term exactly and the intersite
interactions within the mean-field approximation. Our investigation of the
general case taking into account for the first time the effects of
longer-ranged density-density interaction (repulsive and attractive) as well as
possible phase separations shows that, depending on the values of the
interaction parameters and the electron concentration, the system can exhibit
not only several homogeneous charge ordered (CO) phases, but also various phase
separated states (CO-CO and CO-nonordered). One finds that the model considered
exhibits very interesting multicritical behaviours and features, including
among others bicritical, tricritical, critical-end and isolated critical
points.Comment: 12 pages, 7 figures; final version, pdf-ReVTeX; corrected typos in
reference; submitted to Journal of Physics: Condensed Matte
Phase separation in a lattice model of a superconductor with pair hopping
We have studied the extended Hubbard model with pair hopping in the atomic
limit for arbitrary electron density and chemical potential. 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 model can be treated as a simple
effective model of a superconductor with very short coherence length in which
electrons are localized and only electron pairs have possibility of
transferring. The phase diagrams and thermodynamic properties of this model
have been determined within the variational approach, which treats the on-site
interaction term exactly and the intersite interactions within the mean-field
approximation. We have also obtained rigorous results for a linear chain (d=1)
in the ground state. Moreover, at T=0 some results derived within the random
phase approximation (and the spin-wave approximation) for d=2 and d=3 lattices
and within the low density expansions for d=3 lattices are presented. Our
investigation of the general case (as a function of the electron concentration
and as a function of the chemical potential) shows that, depending on the
values of interaction parameters, the system can exhibit not only the
homogeneous phases: superconducting (SS) and nonordered (NO), but also the
phase separated states (PS: SS-NO). The system considered exhibits interesting
multicritical behaviour including tricritical points.Comment: 15 pages, 9 figures; pdf-ReVTeX, final version, corrected typos;
submitted to Journal of Physics: Condensed Matte
Interplay and competition between superconductivity and charge orderings in the zero-bandwidth limit of the extended Hubbard model with pair hopping and on-site attraction
This is an author-created, un-copyedited version of an article accepted for publication in Journal of Superconductivity and Novel Magnetism.We present studies of an effective model which is a simple generalization of the standard model of a local pair superconductor with on-site pairing (i.e., the model of hard core bosons on a lattice) to the case of finite pair binding energy. The tight binding Hamiltonian consists of (i) the effective on-site interaction U, (ii) the intersite density-density interactions W between nearest-neighbours, and (iii) the intersite charge exchange term I, determining the hopping of electron pairs between nearest-neighbour sites. In the analysis of the phase diagrams and thermodynamic properties of this model we treat the intersite interactions within the mean-field approximation. Our investigations of the U0 case show that, depending on the values of interaction parameters, the system can exhibit three homogeneous phases: superconducting (SS), charge-ordered (CO) and nonordered (NO) as well as the phase separated SS-CO state.National Science Center (NCN) as a research project in years 2011-2013, under grant No. DEC-2011/01/N/ST3/00413;
European Commission and Ministry of Science and Higher Education (Poland) - partial financial support from European Social Fund – Operational
Programme "Human Capital" – POKL.04.01.01-00-133/09-00 – "Proinnowacyjne kształcenie, kompetentna kadra, absolwenci przyszłości";
The Fundation of Adam Mickiewicz University in Pozna
The magnetic field induced phase separation in a model of a superconductor with local electron pairing
This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condensed Matter.
IOP Publishing Ltd. is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.
The Version of Record is available online at http://dx.doi.org/10.1088/0953-8984/25/6/065603We 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.National Science Center (NCN) as a research project in years 2011-2013, under grant No. DEC-2011/01/N/ST3/00413; European Commission and Ministry of Science and Higher Education (Poland) - partial financial support from European Social Fund – Operational Programme "Human Capital" – POKL.04.01.01-00-133/09-00 – "Proinnowacyjne kształcenie, kompetentna kadra, absolwenci przyszłości"; The Fundation of Adam Mickiewicz University in Pozna