Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Current instability and single-mode THz generation in ungated
  two-dimensional electron gas   We analyze the current instability of the steady state with a direct current
for an ungated two-dimensional(2D) electron layer for arbitrary current and the
carrier scattering strength. We demonstrate the possibility of single-mode
generator operating in terahertz frequency range.

19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin