Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Superconductivity induced by hydrogen anion substitution in 1111-type
  iron arsenides   Hydrogen is the simplest bipolar element and its valence state can be
controlled from +1 to -1. We synthesized the 1111-type CaFeAsH and LnFeAsO1-xHx
(Ln = lanthanide) with the ZrCuSiAs type structure by a high-pressure synthesis
method. The position and valence state of the substituted H were determined by
neutron diffraction and density functional theory calculations. The close
similarity in the structural and electrical properties of CaFeAsH and CaFeAsF
indicated the formation of the hydride ion (H-), which is isovalent with the
fluoride ion (F-), in the 1111-type iron arsenides. When some of the O2- ions
in LnFeAsO are replaced by H-, superconductivity is induced by electron doping
to the FeAs-layer to maintain charge neutrality. Since the substitution limit
of hydrogen in LnFeAsO (x~0.5) is much higher than that of fluorine (x~0.2),
the hydrogen substitution technique provides an effective pathway for
high-density electron-doping, making it possible to draw the complete
electronic phase diagram of LnFeAsO. The x-T diagrams of LnFeAsO1-xHx (Ln = La,
Ce, Sm, Gd) have a wide superconducting (SC) region spanning the range x = 0.04
to 0.4, which is far from the parent antiferromagnetic region near x = 0.0. For
Ln=La, another SC dome region was found in the range x = ~ 0.2 to ~0.5 with a
maximum Tc = 36 K, in addition to a conventional SC dome located at x ~0.08
with maximum Tc = 29 K. Density functional theory calculations performed for
LaFeAsO1-xHx indicated that the newly observed Tc is correlated with the
appearance of degeneration of the Fe 3d bands (dxy, dyz and dzx), which is
caused not only by regularization of the tetrahedral shape of FeAs4 due to
chemical pressure effects but also by selective band occupation with doped
electrons. In this article, we review the recent progress of superconductivity
in iron (oxy)arsenides and related compounds induced by hydrogen substitution.

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The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci