Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Infrared Hall conductivity of Na$_{0.7}$CoO$_2$   We report infrared Hall conductivity $\sigma_{xy}(\omega)$ of
Na$_{0.7}$CoO$_2$ thin films determined from Faraday rotation angle
$\theta_{F}$ measurements. $\sigma_{xy}(\omega)$ exhibits two types of hole
conduction, Drude and incoherent carriers. The coherent Drude carrier shows a
large renormalized mass and Fermi liquid-like behavior of Hall scattering rate,
$\gamma_{H} \sim aT^{2}$. The spectral weight is suppressed and disappears at T
= 120K. The incoherent carrier response is centered at mid-IR frequency and
shifts to lower energy with increasing T. Infrared Hall constant is positive
and almost independent of temperature in sharp contrast with the dc-Hall
constant.

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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: cs
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ