Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geometry fluctuations in a two-dimensional quantum antiferromagnet   The paper considers the effects of random fluctuations of the local spin
connectivities (fluctuations of the geometry) on ground state properties of a
two-dimensional quantum antiferromagnet. We analyse the behavior of spins
described by the Heisenberg model as a function of what we call phason flip
disorder, following a terminology used for aperiodic systems. The calculations
were carried out both within linear spin wave theory and using quantum Monte
Carlo simulations. An "order by disorder" phenomenon is observed in this model,
wherein antiferromagnetism is found to be enhanced by phason disorder. The
value of the staggered order parameter increases with the number of defects,
accompanied by an increase in the ground state energy of the system.

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The categories of this paper are: astro-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc