Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Triplet excitations in the frustrated spin ladder
  Li$_2$Cu$_2$O(SO$_4$)$_2$   Magnetic excitations of the recently discovered frustrated spin-1/2 two-leg
ladder system Li$_2$Cu$_2$O(SO$_4$)$_2$ are investigated using inelastic
neutron scattering, magnetic susceptibility and infrared absorption
measurements. Despite the presence of a magnetic dimerization concomitant with
the tetragonal-to-triclinic structural distortion occurring below 125 K,
neutron scattering experiments reveal the presence of dispersive triplet
excitations above a spin gap of $\Delta = 10.6$ meV at 1.5 K, a value
consistent with the estimates extracted from magnetic susceptibility. The
likely detection of these spin excitations in infrared spectroscopy is
explained by invoking a dynamic Dzyaloshinskii-Moriya mechanism in which light
is coupled to the dimer singlet-to-triplet transition through an optical
phonon. These results are qualitatively explained by exact diagonalization and
higher-order perturbation calculations carried out on the basis of the
dimerized spin Hamiltonian derived from first-principles.

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The categories of this paper are: astro-ph
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The categories of this paper are: cmp-lg
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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: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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The categories of this paper are: math
0
The categories of this paper are: hep-ph
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The categories of this paper are: atom-ph
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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: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con