Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Synthesis, crystal structure and superconductivity in
  Rb$Ln_2$Fe$_4$As$_4$O$_2$ ($Ln$ = Sm, Tb, Dy and Ho)   We have synthesized four iron-based oxyarsenide superconductors
Rb$Ln_2$Fe$_4$As$_4$O$_2$ ($Ln$ = Sm, Tb, Dy and Ho) resulting from the
intergrowth of RbFe$_2$As$_2$ and $Ln$FeAsO. It is found that the lattice match
between RbFe$_2$As$_2$ and $Ln$FeAsO is crucial for the phase formation. The
structural intergrowth leads to double asymmetric Fe$_2$As$_2$ layers that are
separated by insulating $Ln_2$O$_2$ slabs. Consequently, the materials are
intrinsically doped at a level of 0.25 holes/Fe-atom and, bulk
superconductivity emerges at $T_\mathrm{c}$ = 35.8, 34.7, 34.3 and 33.8 K,
respectively, for $Ln$ = Sm, Tb, Dy and Ho. Investigation on the correlation
between crystal structure and $T_\mathrm{c}$ suggests that interlayer couplings
may play an additional role for optimization of superconductivity.

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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: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
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The categories of this paper are: stat
1
The categories of this paper are: cs
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The categories of this paper are: nucl-ex
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The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: dg-ga