Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical signatures of phase transitions and structural modulation in
  elemental tellurium under pressure   A room-temperature infrared spectroscopy study of elemental tellurium at
pressures up to 8.44 GPa in the energy range 0.015-2 eV is reported. Optical
signatures of the high-pressure polymorphs are investigated and compared to the
results of density-functional band-structure calculations. A Drude peak is
first seen in the optical conductivity around 3.5 GPa indicating a
semiconductor-to-metal transition within trigonal Te-I. A sharp increase in the
Drude spectral weight and dc-conductivity around 4.3 GPa signals the
transformation toward the triclinic Te-II polymorph. An absorption peak around
0.15 eV appears above 5 GPa concomitant with the gradual transformation of
Te-II into the structurally similar but incommensurately modulated Te-III.
Microscopically, this peak can only be reproduced within a sufficiently large
commensurate approximant, suggesting the low-energy optical response as a
fingerprint of the structural modulation.

3
The categories of this paper are: physics
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int