Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fe-vacancy order and superconductivity in PbO-type tetragonal
  {\beta}-Fe1-xSe   Several superconducting transition temperatures in the range of 30-40 K were
reported in the recently discovered intercalated FeSe sytem (A1-xFe2-ySe2, A =
K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively
decided, more than one magnetic phase with particular orders of iron vacancy
and/or potassium vacancy were identified, and some were argued to be the parent
phase. Here we show the discovery of the presence and ordering of iron vacancy
in nonintercalated FeSe (PbO-type tetragonal {\beta}-Fe1-xSe). Three types of
iron-vacancy order were found through analytical electron microscopy, and one
was identified to be nonsuperconducting and magnetic at low temperature. This
discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive
in Fe-Se related superconductors. In addition, the magnetic {\beta}-Fe1-xSe
phases with particular iron-vacancy orders are more likely to be the parent
phase of FeSe superconducting system, instead of the previously assigned
{\beta}-Fe1+{\delta}Te.

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The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
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The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
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The categories of this paper are: supr-con
2
The categories of this paper are: math
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: astro-ph
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The categories of this paper are: nlin