Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Planar pyrochlore: a strong-coupling analysis   Recent investigations of the two-dimensional spin-1/2 checkerboard lattice
favor a valence bond crystal with long range quadrumer order [J.-B. Fouet et
al., preprint cond-mat/0108070]. Starting from the limit of isolated
quadrumers, we perform a complementary analysis of the evolution of the
spectrum as a function of the inter quadrumer coupling j using both, exact
diagonalization (ED) and series expansion (SE) by continuous unitary
transformation. We compute (i) the ground state energy, (ii) the elementary
triplet excitations, (iii) singlet excitations on finite systems and find very
good agreement between SE and ED. In the thermodynamic limit we find a ground
state energy substantially lower than documented in the literature. The
elementary triplet excitation is shown to be gapped and almost dispersionless,
whereas the singlet sector contains strongly dispersive modes. Evidence is
presented for the low energy singlet excitations in the spin gap in the
vicinity of j=1 to result from a large downward renormalization of local
high-energy states.

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The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
0
The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an