Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Absence of a structural transition up to 40 Gpa in MgB2 and the
  relevance of magnesium non-stoichiometry   We report measurements on MgB2 up to ~40GPa. Increasing pressure yields a
monotonous decrease of the lattice parameters and of the c/a ratio, but no
structural transition down to parameters smaller than those of AlB2. The
transition superconducting temperature also decreases with temperature in a
sample dependent way. The results are explained by an increase of the filling
of the 2D pxy bands with pressure, the Mg stoichiometry determining the
starting position of the Fermi level. Our measurements indicate that these hole
bands are the relevant ones for superconductivity.

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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: stat
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The categories of this paper are: quant-ph
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
2
The categories of this paper are: math
22
The categories of this paper are: chao-dyn