Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pressure Tuning of an Ionic Insulator into a Heavy Electron Metal: An
  Infrared Study of YbS   Optical conductivity [$\sigma(\omega)$] of YbS has been measured under
pressure up to 20 GPa. Below 8 GPa, $\sigma(\omega)$ is low since YbS is an
insulator with an energy gap between fully occupied 4$f$ state and unoccupied
conduction ($c$) band. Above 8 GPa, however, $\sigma(\omega)$ increases
dramatically, developing a Drude component due to heavy carriers and
characteristic infrared peaks. It is shown that increasing pressure has caused
an energy overlap and hybridization between the $c$ band and 4$f$ state, thus
driving the initially ionic and insulating YbS into a correlated metal with
heavy carriers.

20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat