Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nature of the insulating phases in the half-filled ionic Hubbard model   We investigate the ground-state phase diagram of the one-dimensional "ionic"
Hubbard model with an alternating periodic potential at half-filling by
numerical diagonalization of finite systems with the Lanczos and density matrix
renormalization group (DMRG) methods. We identify an insulator-insulator phase
transition from a band to a correlated insulator with simultaneous charge and
bond-charge order. The transition point is characterized by the vanishing of
the optical excitation gap while simultaneously the charge and spin gaps remain
finite and equal. Indications for a possible second transition into a
Mott-insulator phase are discussed.

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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: alg-geom
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The categories of this paper are: physics
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: hep-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg