Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anisotropic resistivity and Hall effect in MgB2 single crystals   We report resistivity and the Hall effect measurements in the normal and
superconducting states of MgB2 single crystal. The resistivity has been found
to be anisotropic with slightly temperature dependent resistivity ratio of
about 3.5. The Hall constant, with a magnetic field parallel to the Mg and B
sheets is negative in contrast to the hole-like Hall response with a field
directed along the c-axis indicating presence of both types of charge carriers
and, thus, multi-band electronic structure of MgB2. The Hall effect in the
mixed state shows no sign change anomaly reproducing the Hall effect behavior
in clean limit type-II superconductors.

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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
2
The categories of this paper are: math
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
3
The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org