Hideo Hosono talks with
ScienceWatch.com and answers a few questions about
this month's Emerging Research Front Paper in the field of
Space Science. The author has also sent along images
of their work.
Article: Iron-based layered superconductor
La[O1-xFx]FeAs (x=0.05-0.12) with T-c=26 K
Journal: J AM CHEM SOC, 130 (11): 3296-+ MAR 19 2008
Addresses: Tokyo Inst Technol, Frontier Res Ctr, JST, ERATO
SORST,Midori Ku, Mail Box S2-13,4259 Nagatsuta, Yokohama,
Kanagawa 2268503, Japan.
Tokyo Inst Technol, Frontier Res Ctr, JST, ERATO
SORST,Midori Ku, Yokohama, Kanagawa 2268503, Japan.
(addresses have been truncated.)
Why do you think your paper is highly
Long-range ordering of spin moments competes with the emergence of
superconductivity which originates from the formation of Cooper pairs.
Thus, it was widely believed that iron, a representative ferromagnetic
metal, was the last element required for superconductivity.
However, this paper reported that high Tc of 32K (on set) was discovered in
layered lanthanum iron oxyarsenide. This Tc was the third among the
superconductors reported so far, the top is a cuprate, the second is MgB2.
No new high-Tc material was found since the discovery of MgB2 in 2001 by
Professor Jun Akimitsu's group at Aoyama-Gakuin University in Tokyo. I
think that breaking this widely-perceived idea and an unexpected high Tc
are the primary causes of the high citation rate of this paper.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
This paper reports on the discovery of a new high Tc superconductor in
F-doped LaFeAsO with layered structure and a variation of Tc with doped
Would you summarize the significance of your paper in
A brand new high-Tc superconductor was discovered in a layered iron
oxyarsenide compound. No superconductivity was observed in F-free LaFeAsO,
but only upon the partial replacement of oxygen with fluorine, which means
electron-doping, Tc appeared, and increased to 32K(on-set) or
26K(mid-point) at the optimal F-content (~10%). See Figures 1 & 2.
How did you become involved in this research and were
there any particular problems encountered along the way?
Our major concern was a new transparent oxide semiconductor. We extended
our research from transparent semiconductors to magnetic semiconductors by
exploring a new 3d series transition metal–based compound with
low-dimensional crystal structure. As a consequence, in 2006 and 2007, we
found superconductivity in LaFePO (Tc=4K) and LaNiPO (Tc=3K). Interestingly
enough, both Fe and Ni are ferromagnetic metals. These compounds exhibit
superconductivity without carrier doping, but LaFeAsO is more resistive and
does not show Tc. However, F-doping to oxygen ion sites induced
superconductivity and raised Tc to 32K.
Where do you see your research leading in the
This paper inspired intensive research on iron-based superconductors all
across the world. Tc was raised to 55K, which was the highest, except in
cuprates. In the past half-year, at least seven international workshops or
special symposia have been held in Japan, Europe, the US, and China. Also,
two special journal issues are scheduled to be published in December, 2008
and January, 2009. This paper revitalized the intensive research into
high-Tc superconductors (See Figure 3).
Do you foresee any social or political implications for
Research projects on iron-based superconductors have already started or are
ready to begin in Japan, China, Germany, Europe, and the US. Our discovery
of Iron-based high-Tc superconductors smashed the monopoly of CuO2 for
high-Tc which had continued over the past 20 years. It has turned out that
several unique properties are favored for application, among these are high
critical magnetic fields and the less anisotropic nature of current flow.
Hideo Hosono, Ph.D.
Materials and Structures Laboratory
Tokyo Institute of Technology
Yokohama, Japan Web |