Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Some properties of the model of a superconductor with pair hopping and
  magnetic interactions at half-filling   We present our preliminary studies of an effective model of a superconductor
with short coherence length involving magnetic interactions. The Hamiltonian
considered consists of (i) the effective on-site interaction U, (ii) the
intersite magnetic exchange interactions (Jz, Jxy) between nearest-neighbors
and (iii) the intersite charge exchange term I, determining the hopping of
electron pairs between nearest-neighbor sites. In the analysis of the phase
diagrams and thermodynamic properties of this model for half-filling (n=1) we
have adopted the variational approach, which treats the on-site interaction
term exactly and the intersite interactions within the mean-field
approximation. One finds that the system considered can exhibit very
interesting multicritical behaviors (including tricritical, critical-end and
bicritical points) caused by the competition between magnetism and
superconductivity, even for n=1. Our investigations show that, depending on the
values of interaction parameters, the system at half-filling can exhibit three
homogeneous phases: superconducting (SS), (anti-)ferromagnetic (F) and
nonordered (NO). The transitions between ordered phases (SS, F) and the NO
phase can be first order as well as second order ones, whereas SS-F transition
is first order one. Temperature dependencies of the order parameters and
thermodynamic properties of the system at the sequence of transitions: SS-F-NO
with increasing temperature for J/I=0.3, U/I0 = 0.69 and n=1 are also
presented.

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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin