Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Meissner effect in nonstandard superconductors   It was recently pointed out that so-called "superhydrides", hydrogen-rich
materials that appear to become superconducting at high temperatures and
pressures, exhibit physical properties that are different from both
conventional and unconventional standard type I and type II superconductors
[1,2]. Here we consider magnetic field expulsion in the first material in this
class discovered in 2015, sulfur hydride [3]. A nuclear resonant scattering
experiment has been interpreted as demonstration that the Meissner effect takes
place in this material [4,5]. Here we point out that the observed effect, under
the assumption that the system is in thermodynamic equilibrium, implies a
Meissner pressure [6] in this material that is {\it much larger} than that of
standard superconductors. This suggests that hydride superconductors are
qualitatively different from the known standard superconductors {\it if} they
are superconductors.

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The categories of this paper are: chem-ph
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
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The categories of this paper are: bayes-an
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex