Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-frequency nonlinear transport and photogalvanic effects in
  two-dimensional topological insulators   Excitation of a topological insulator by a high-frequency electric field of a
laser radiation leads to a dc electric current in the helical edge channel
whose direction and magnitude are sensitive to the radiation polarization and
depend on the physical properties of the edge. We present an overview of
theoretical and experimental studies of such edge photoelectric effects in
two-dimensional topological insulators based on semiconductor quantum wells.
First, we give a phenomenological description of edge photocurrents, which may
originate from the photogalvanic effects or the photon drag effects, for edges
of all possible symmetry. Then, we discuss microscopic mechanisms of
photocurrent generation for different types of optical transitions involving
helical edge states. They include direct and indirect optical transitions
within the edge channel and edge-to-bulk optical transitions.

28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con