Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Undoped Electron-Hole Bilayers in a GaAs/AlGaAs Double Quantum Well   We present the fabrication details of completely undoped electron-hole
bilayer devices in a GaAs/AlGaAs double quantum well heterostructure with a 30
nm barrier. These devices have independently tunable densities of the
two-dimensional electron gas and two-dimensional hole gas. We report
four-terminal transport measurements of the independently contacted electron
and hole layers with balanced densities from $1.2 \times 10^{11}$cm$^{-2}$ down
to $4 \times 10^{10}$ cm$^{-2}$ at $T = 300 mK$. The mobilities can exceed $1
\times 10^{6}$ cm$^{2}$ V$^{-1}$ s$^{-1}$ for electrons and $4 \times 10^{5}$
cm$^{2}$ V$^{-1}$ s$^{-1}$ for holes.

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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: ao-sci
29
The categories of this paper are: funct-an
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The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: econ
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The categories of this paper are: hep-th