Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anisotropy of the Energy Gap in the Insulating Phase of the U-t-t'
  Hubbard Model   We apply a diagrammatic expansion method around the atomic limit (U >> t) for
the U-t-t' Hubbard model at half filling and finite temperature by means of a
continued fraction representation of the one-particle Green's function. From
the analysis of the spectral function A(\vec{k},\omega) we find an energy
dispersion relation with a (cos k_x-cos k_y)^2 modulation of the energy gap in
the insulating phase. This anisotropy is compared with experimental ARPES
results on insulating cuprates.

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The categories of this paper are: chem-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: acc-phys
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: nlin
2
The categories of this paper are: math
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
3
The categories of this paper are: physics
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The categories of this paper are: eess