[Authors' affiliations: Nihon University, Tokyo, Japan; Tokyo Institute of
Technology, Japan]
Abstract: "The iron- and nickel-based layered compounds
LaOFeP and LaONiP have recently been reported to exhibit low-temperature
superconducting phases with transition temperatures Tc of 3 and 5 K,
respectively. Furthermore, a large increase in the midpoint Tc of up to
similar to 26 K has been realized in the isocrystalline compound LaOFeAs on
doping of fluoride ions at the O2- sites (LaO1-xFxFeAs). Experimental
observations and theoretical studies suggest that these transitions are
related to a magnetic instability, as is the case for most superconductors
based on transition metals. In the copper-based
high-temperature
superconductors, as well as in LaOFeAs, an increase in Tc is often
observed as a result of carrier doping in the two-dimensional electronic
structure through ion substitution in the surrounding insulating layers,
suggesting that the application of external pressure should further
increase T-c by enhancing charge transfer between the insulating and
conducting layers. The effects of pressure on these iron oxypnictide
superconductors may be more prominent than those in the copper-based
systems, because the As ion has a greater electronic polarizability, owing
to the covalency of the Fe-As chemical bond, and, thus, is more
compressible than the divalent O2- ion. Here we report that increasing the
pressure causes a steep increase in the onset Tc of F-doped LaOFeAs, to a
maximum of similar to 43 K at similar to 4 GPa. With the exception of the
copper-based high-Tc superconductors, this is the highest Tc reported to
date. The present result, together with the great freedom available in
selecting the constituents of isocrystalline materials with the general
formula LnOTMPn (Ln, Y or rare-earth metal; TM, transition metal; Pn,
group-V, 'pnicogen', element), indicates that the layered iron oxypnictides
are promising as a new material platform for further exploration of
high-temperature superconductivity."
This 2008 report from Nature on an iron-based superconductor was
cited 39 times in current journal articles
indexed by Clarivate during March-April 2009. For the fourth
consecutive bimonthly period, this paper registers as the #3 most-cited of
any non-review paper published in the last two years and coded as chemistry
(although by now the paper has also logged numerous citations recorded in
physics journals). In fact, for the duration of this paper's run at #3, the
first- and second-most-cited chemistry papers have also centered on
iron-based superconductivity, with those slots consecutively occupied by
the same two reports. Prior to the most recent bimonthly count, citations
to the Takahashi et al. paper have accrued as follows:
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