Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pressure-induced metallization and structural phase transition of the
  Mott-Hubbard insulator TiOBr   We investigated the pressure-dependent optical response of the
low-dimensional Mott-Hubbard insulator TiOBr by transmittance and reflectance
measurements in the infrared and visible frequency range. A suppression of the
transmittance above a critical pressure and a concomitant increase of the
reflectance are observed, suggesting a pressure-induced metallization of TiOBr.
The metallic phase of TiOBr at high pressure is confirmed by the presence of
additional excitations extending down to the far-infrared range. The
pressure-induced metallization coincides with a structural phase transition,
according to the results of x-ray powder diffraction experiments under
pressure.

36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
3
The categories of this paper are: physics
18
The categories of this paper are: econ
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
19
The categories of this paper are: eess