Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electron spin relaxation in bulk GaAs for doping densities close to the
  metal-to-insulator transition   We have measured the electron spin relaxation rate and the integrated spin
noise power in n-doped GaAs for temperatures between 4 K and 80 K and for
doping concentrations ranging from 2.7 x 10^{-15} cm^{-3} to 8.8 x 10^{-16}
cm^{-3} using spin noise spectroscopy. The temperature dependent measurements
show a clear transition from localized to free electrons for the lower doped
samples and confirm mainly free electrons at all temperatures for the highest
doped sample. While the sample at the metal-insulator-transition shows the
longest spin relaxation time at low temperatures, a clear crossing of the spin
relaxation rates is observed at 70 K and the highest doped sample reveals the
longest spin relaxation time above 70 K.

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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th