Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orbital Symmetry and Orbital Excitations in High-$T_c$ Superconductors   We discuss a few possibilities of high-$T_c$ superconductivity with more than
one orbital symmetry contributing to the pairing. First, we show that the high
energies of orbital excitations in various cuprates suggest a simplified model
with a single orbital of $x^2-y^2$ symmetry doped by holes. Next, several
routes towards involving both $e_g$ orbital symmetries for doped holes are
discussed: (i) some give superconductivity in a CuO$_2$ monolayer on Bi2212
superconductors, Sr$_2$CuO$_{4-\delta}$, Ba$_2$CuO$_{4-\delta}$, while (ii)
others as nickelate heterostructures or Eu$_{2-x}$Sr$_x$NiO$_4$, could in
principle realize it as well. At low electron filling of Ru ions, spin-orbital
entangled states of $t_{2g}$ symmetry contribute in Sr$_2$RuO$_4$. Finally,
electrons with both $t_{2g}$ and $e_g$ orbital symmetries contribute to the
superconducting properties and nematicity of Fe-based superconductors,
pnictides or FeSe. Some of them provide examples of orbital-selective Cooper
pairing.

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The categories of this paper are: alg-geom
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The categories of this paper are: astro-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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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: nlin
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The categories of this paper are: adap-org
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-alg
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an