Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoproduction in semiconductors by onset of magnetic field   The energy bands of a semiconductor are lowered by an external magnetic
field. When a field is switched on, the straight-line trajectories near the top
of the occupied valence band are curved into Landau orbits and Bremsstrahlung
is emitted until the electrons have settled in their final Fermi distribution.
We calculate the radiated energy, which should be experimentally detectable,
and suggest that a semiconductor can be cooled by an oscillating magnetic
field.

25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
6
The categories of this paper are: astro-ph
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org