Archive ScienceWatch

Hideo Hosono talks with 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.
Hosono Article: Iron-based layered superconductor La[O1-xFx]FeAs (x=0.05-0.12) with T-c=26 K
Authors: Kamihara, Y;Watanabe, T;Hirano, M;Hosono, H
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 cited?

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.

Figure 1: +details
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Figure 2:
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Figure 3:
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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 F-contents.

Would you summarize the significance of your paper in layman's terms?

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 future?

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 your research?

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 | See also

Related: Research Front Map on LAYERED SUPERCONDUCTORS (from Space Science, November 2008)

Keywords: Iron-based layered superconductor La[O1-xFx]FeAs (x=0.05-0.12) with T-c=26 K.

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2008 : December 2008 : Hideo Hosono