Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing two-subband systems in a quantizing magnetic field with
  non-equilibrium phonons   We propose to use phonon absorption spectroscopy to study many-body gaps and
phases of two-subband heterostructures in the quantum Hall regime. Implications
of the spin-orbit interaction for phonon absorption in this system are
considered.

3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg