Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Evidence for flat zero-energy bands in bilayer graphene with a periodic
  defect lattice
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys