Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Temperature dependence of the optical phonon reflection band in GaP   We explore the effect of temperatures between 80 and 720 K on the energy and
linewidth of zone-center transverse (TO) and longitudinal (LO) optical phonons
in bulk gallium phosphide (GaP) using Fourier transform infrared ellipsometry
from 0.03 to 0.60 eV. We extract the optical phonon parameters of GaP by
fitting the ellipsometric angles with the Lowndes-Gervais model, which applies
two different broadening parameters to the TO and LO phonons. In GaP, the
two-phonon density of states is larger for the decay of TO phonons than for LO
phonons. Therefore, we observed a larger TO phonon broadening (compared to the
LO phonon) and an asymmetric reststrahlen line shape. This would lead to a
negative imaginary part of the dielectric function just above the LO phonon
energy, but the addition of two-phonon absorption avoids this. We find a
temperature dependent redshift and broadening of TO and LO phonons with
increasing temperature due to thermal expansion and anharmonic phonon-phonon
scattering, involving three and four phonon decay processes. We also
investigate the temperature-dependence of the high-frequency dielectric
constant. Its variation is explained by thermal expansion and the temperature
dependence of the Penn gap.

31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
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The categories of this paper are: adap-org
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
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The categories of this paper are: funct-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: physics
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The categories of this paper are: atom-ph
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The categories of this paper are: econ