Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A magnetic barrier in confined two-dimensional electron gases:
  Nanomagnetometers and magnetic switches
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph