Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Negative terahertz conductivity in disordered graphene bilayers with
  population inversion
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg