Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ballistic electron transport exceeding 160 microns in an undoped
  GaAs/AlGaAs FET   We report measurements of GaAs/AlGaAs undoped field-effect transistors in
which two-dimensional electron gases (2DEGs) of exceptional quality and
versatility are induced without modulation doping. Electron mobilities at T=4.2
K and density 3 E11 /cm^2 exceed 4 E6 cm^2/Vs. At lower temperatures, there is
an unusually large drop in scattering, such that the mobility becomes too high
to measure in 100 micron samples. Below T=2.5 K, clear signatures of ballistic
travel over path lengths in excess of 160 microns are observed in magnetic
focusing experiments. Multiple reflections at the edges of the 2DEG indicate a
high degree of specularity.

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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
25
The categories of this paper are: patt-sol