Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Transport and optics at the node in a nodal loop semimetal   We use a Kubo formalism to calculate both A.C. conductivity and D.C.
transport properties of a dirty nodal loop semimetal. The optical conductivity
as a function of photon energy $\Omega $, exhibits an extended flat background
$\sigma^{BG}$ as in graphene provided the scattering rate $\Gamma$ is small as
compared to the radius of the nodal ring $b$ (in energy units). Modifications
to the constant background arise for $\Omega\le \Gamma $ and the minimum D.C.
conductivity $\sigma^{DC} $ which is approached as $\Omega^2/\Gamma^2$ as
$\Omega\rightarrow0$, is found to be proportional to
$\frac{\sqrt{\Gamma^2+b^2}}{v_{F}}$ with $v_{F}$ the Fermi velocity. For $b=0$
we recover the known three-dimensional point node Dirac result $\sigma^{DC}\sim
\frac{\Gamma}{v_{F}}$ while for $b>\Gamma$, $\sigma^{DC}$ becomes independent
of $\Gamma$ (universal) and the ratio
$\frac{\sigma^{DC}}{\sigma^{BG}}=\frac{8}{\pi^2}$ where all reference to
material parameters has dropped out. As $b$ is reduced and becomes of the order
$\Gamma$, the flat background is lost as the optical response evolves towards
that of a three-dimensional point node Dirac semimetal which is linear in
$\Omega$ for the clean limit. For finite $\Gamma$ there are modifications from
linearity in the photon region $\Omega\le \Gamma$. When the chemical potential
$\mu$ (temperature $T$) is nonzero the D.C. conductivity increases as
$\mu^2/\Gamma^2$($T^2/\Gamma^2$) for $\mu/\Gamma$ $(T/\Gamma)\le 1$. For larger
values of $\mu>\Gamma$ away from the nodal region the conductivity shows a
Drude like contribution about $\Omega\approxeq 0$ which is followed by a dip in
the Pauli blocked region $\Omega \le 2\mu$ after which it increases to merge
with the flat background (two-dimensional graphene like) for $\mu< b$ and to
the quasilinear (three-dimensional point node Dirac) law for $\mu> b$.

16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
1
The categories of this paper are: cs
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The categories of this paper are: adap-org
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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: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc