Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electronic and phonon excitations in {\alpha}-RuCl$_3$   We report on THz, infrared reflectivity and transmission experiments for wave
numbers from 10 to 8000 cm$^{-1}$ ($\sim$ 1 meV - 1 eV) and for temperatures
from 5 to 295 K on the Kitaev candidate material {\alpha}-RuCl$_3$. As reported
earlier, the compound under investigation passes through a first-order
structural phase transition, from a monoclinic high-temperature to a
rhombohedral low-temperature phase. The phase transition shows an extreme and
unusual hysteretic behavior, which extends from 60 to 166 K. In passing this
phase transition, in the complete frequency range investigated we found a
significant reflectance change, which amounts almost a factor of two. We
provide a broadband spectrum of dielectric constant, dielectric loss and
optical conductivity from the THz to the mid infrared regime and study in
detail the phonon response and the low-lying electronic density of states. We
provide evidence for the onset of an optical energy gap, which is of order 200
meV, in good agreement with the gap derived from measurements of the DC
electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue
shift on increasing temperatures.

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The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
14
The categories of this paper are: math-ph
2
The categories of this paper are: math