Huiqiu Yuan talks with
ScienceWatch.com and answers a few questions about
this month's New Hot Paper in the field of
Physics.
Article Title: Nearly isotropic superconductivity in
(Ba,K)Fe2As2
Authors: Yuan, HQ;Singleton, J;Balakirev,
FF;Baily, SA;Chen, GF;Luo, JL;Wang, NL
Journal: NATURE, Volume: 457, Issue: 7229, Page: 565-568, Year:
JAN 29 2009
* Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R
China.
* Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R
China.
* Los Alamos Natl Lab, NHMFL, MS E536, Los Alamos, NM 87545
USA.
* Chinese Acad Sci, Beijing Natl Lab Condensed Matter Phys,
Beijing 10080, Peoples R China. (addresses have been
truncated.)
Why do you think your paper is highly cited?
Does it describe a new discovery, methodology, or synthesis of
knowledge?
This paper reported on a new physical phenomenon, the observation of nearly
isotropic superconductivity in a layered superconductor
(Ba,K)Fe2As2. Such an experiment has been extended to
many other systems, showing that the weak anisotropy is a rather common
feature in iron-based
superconductors.
For layered compounds, their electronic properties are usually anisotropic
as a result of two-dimensional band structure which determines the
dispersion of electrons in the momentum space.
Most of the high Tc superconductors, e.g., the cuprate oxides, crystallize
in a layered crystal structure, showing rather anisotropic properties.
Therefore, two-dimensionality has been regarded as a prerequisite condition
for achieving high-temperature superconductivity.
"...our findings indicate that reduced dimensionality
is not a necessary prerequisite for high temperature
superconductivity, therefore, providing an alternative
route to enhance the superconducting transition
temperature."
However, our discovery of three-dimensional superconductivity in a layered
compound strikingly differs from such an expectation and might provide an
alternative approach to enhance superconducting transition temperature.
Moreover, these findings are fundamental for understanding the mechanism of
superconductivity in iron pnictides.
Would you summarize the significance of your paper
in layman's terms?
The upper critical field reflects the robustness of superconductivity
against magnetic field. The potential application of a superconductor is
largely determined by the value of the upper critical field and the degree
of its anisotropy.
In our paper, we found that (Ba,K)Fe2As2 possesses
not only a very large (over 65 T) but also nearly isotropic upper critical
field, suggesting that the iron pnictides might have promising
applications.
On the other hand, the observation of three-dimensional superconductivity
in the iron pnictides indicates the importance of electronic coupling along
the c-axis, providing a key experimental fact for theoretical
investigation.
How did you become involved in this research, and
were there any problems along the way?
I had been working on the physical properties of correlated materials which
contained pulsed magnetic field. The discovery of superconductivity in
La(O1-xFx)FeAs quickly attracted our attention.
We were the first group to investigate the anisotropy of superconductivity
in iron pnictides using pulsed magnetic field. But we failed at the
beginning because it was extremely difficult to deal with the tiny single
crystals we obtained (the 1111 series).
Later, the successful growth of large single crystals of the 122 series
provided us with a great opportunity to study such an anisotropic effect,
which eventually led to the observation of the nearly isotropic upper
critical field in (Ba,K)Fe2As2, as reported in this
paper.
Where do you see your research leading in the
future?
First, our findings have stimulated theoretical investigations on such a
new phenomenon.
Second, the observations of large upper critical field with weak anisotropy
indicate the promising applications of the iron based superconductors.
Third, our findings show that reduced dimensionality is not a necessary
prerequisite for high temperature superconductivity, therefore, providing
an alternative route to enhance the superconducting transition temperature.
Huiqiu Yuan, Ph.D.
Chang-Jiang Chair Professor
Department of Physics
Zhejiang University
Hangzhou, PRC