Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Series Expansions for Variable Electron Density   We have developed a series expansion method for calculating the
zero-temperature properties of lattice electron models for variable electron
density, i.e. for finite doping away from the half-filled case. This is done by
introducing particle fluctuation terms in both the unperturbed Hamiltonian and
perturbation. The method is demonstrated by application to the 2-chain $t-J$
ladder, where we provide comparison with previous work as well as obtaining a
number of new results.

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The categories of this paper are: cs
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: math
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: nlin
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The categories of this paper are: hep-lat
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas