Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theory of (001) surface and bulk states in
  Y$_{1-y}$Ca$_y$Ba$_2$Cu$_3$O$_{7-\delta}$}   A self-consistent model is developed for the surface and bulk states of thin
Y_{1-y}Ca_yBa_2Cu_3O_{7-\delta} (YCBCO) films. The dispersions of the chain and
plane layers are modelled by tight-binding bands, and the electronic structure
is then calculated for a finite-thickness film. The dopant atoms are treated
within a virtual crystal approximation. Because YCBCO is a polar material,
self-consistent treatment of the long range Coulomb interaction leads to a
transfer of charge between the film surfaces, and to the formation of surface
states. The tight binding band parameters are constrained by the requirement
that the calculated band structure of surface states at CuO$_2$-terminated
surfaces be in agreement with photoemission experiments. The spectral function
and density of states are calculated and compared with experiments. Unlike the
case of Bi_2Sr_2CaCu_2O_8, where the surfaces are believed to be representative
of the bulk, the densities of states at the YCBCO surfaces are shown to be
qualitatively different from the bulk, and are sensitive to doping. The
calculated spectral function agrees closely with both bulk-sensitive and
surface-sensitive photoemission results, while the calculated density of states
for optimally-doped YCBCO agrees closely with tunneling experiments. We find
that some density of states features previously ascribed to competing order can
be understood as band structure effects.

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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin
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The categories of this paper are: econ
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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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: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph