Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Enhancement of superconducting transition temperature of FeSe by
  intercalation of a molecular spacer layer   The recent discovery of high temperature superconductivity in a layered iron
arsenide has led to an intensive search to optimize the superconducting
properties of iron-based superconductors by changing the chemical composition
of the spacer layer that is inserted between adjacent anionic iron arsenide
layers. Until now, superconductivity has only been found in compounds with a
cationic spacer layer consisting of metal ions: Li+, Na+, K+, Ba2+ or a
PbO-type or perovskite-type oxide layer. Electronic doping is usually necessary
to control the fine balance between antiferromagnetism and superconductivity.
Superconductivity has also been reported in FeSe, which contains neutral layers
similar in structure to those found in the iron arsenides but without the
spacer layer. Here we demonstrate the synthesis of Lix(NH2)y(NH3)1-yFe2Se2 (x
~0.6 ; y ~ 0.2), with lithium ions, lithium amide and ammonia acting as the
spacer layer, which exhibits superconductivity at 43(1) K, higher than in any
FeSe-derived compound reported so far and four times higher at ambient pressure
than the transition temperature, Tc, of the parent Fe1.01Se. We have determined
the crystal structure using neutron powder diffraction and used magnetometry
and muon-spin rotation data to determine the superconducting properties. This
new synthetic route opens up the possibility of further exploitation of related
molecular intercalations in this and other systems in order to greatly optimize
the superconducting properties in this family.

20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int