Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical Conductivity of Ortho-II YBa$_2$Cu$_3$O$_6.5$   The Ortho-II phase of YBa$_2$Cu$_3$O$_6.5$ is characterized by a periodic
alternation of empty Cu and filled Cu-O b-axis doubling the unit cell in the a
direction. The extra oxygen in the full chains gives rise to an attractive
potential for the holes in the planes. The planar bands split in two with a gap
opening at the new Brillouin zone boundary $k_x=\pm pi/2$, which we estimate
from LDA calculations. Using a planar model which treats the d-wave
superconductivity in a mean field approximation, we show that interband
transitions produce a strongly anisotropic feature in the optical conductivity
controlled by a region in k-space close to ($\pi/2,\pi/2$). The edge position
of this feature gives information on the temperature dependence of
quasiparticle spectrum in this region. Bilayer splitting would show up as a
double edge shape.

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The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
19
The categories of this paper are: eess
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio