Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical Response in Excitonic Insulating State: Variational Cluster
  Approach   Optical responses in an excitonic insulating (EI) system with strong electron
correlation are studied. We adopt the two-orbital Hubbard model with a finite
energy difference between the two orbitals where the spin state degree of
freedom exists. This model is analyzed by the variational cluster approach. In
order to include the local electron correlation effect, the vertex correction
is taken into account in the formulation of the optical conductivity spectra.
We calculate a finite-temperature phase diagram, in which an EI phase appears
between a low-spin band insulating state and a high-spin Mott insulating state.
Characteristic components of the optical conductivity spectra consisting of a
sharp peak and continuum appear in the EI phase. Integrated intensity almost
follows the order parameter of the EI state, suggesting that this component is
available to identify the EI phases and transitions.

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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: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: atom-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: supr-con
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The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin