Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic Excitation Spectrum of the Square Lattice S=1/2 Heisenberg
  Antiferromagnet K2V3O8   We have explored the magnetic excitation spectrum of the S=1/2 square lattice
Heisenberg antiferromagnet, K2V3O8 using both triple-axis and time-of-flight
inelastic neutron scattering. The long-wavelength spin waves are consistent
with the previously determined Hamiltonian for this material. A small energy
gap of 72+/-9 micro-eV is observed at the antiferromagnetic zone center and the
near-neighbor exchange constant is determined to be 1.08+/-0.03 meV. A finite
ferromagnetic interplanar coupling is observed along the crystallographic
c-axis with a magnitude of Jc=-0.0036+/-0.006 meV. However, upon approaching
the zone boundary, the observed excitation spectrum deviates significantly from
the expectation of linear spin wave theory resulting in split modes at the
(pi/2,pi/2) zone boundary point. The effects of magnon-phonon interaction,
orbital degrees of freedom, multimagnon scattering, and dilution/site
randomness are considered in the context of the mode splitting. Unfortunately,
no fully satisfactory explanation of this phenomenon is found and further
theoretical and experimental work is needed.

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The categories of this paper are: cmp-lg
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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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: alg-geom
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The categories of this paper are: gr-qc