Hong Ding talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of
Physics. The author has also sent along an image of
his work.
Article Title: Observation of
Fermi-surface-dependent nodeless superconducting gaps in
Ba0.6K0.4Fe2As2
Authors: Ding,
H;Richard, P;Nakayama, K;Sugawara, K;Arakane,
T;Sekiba, Y;Takayama, A;Souma, S;Sato, T;Takahashi, T;Wang,
Z;Dai, X;Fang, Z;Chen, GF;Luo, JL;Wang, NL
Journal: EPL, Volume: 83, Issue: 4, Page: art., Year:
no.-47001 2008
* Chinese Acad Sci, Beijing Natl Lab Condensed Matter Phys,
Beijing 100190, Peoples R China.
* Chinese Acad Sci, Beijing Natl Lab Condensed Matter Phys,
Beijing (addresses have been truncated)
Why do you think your paper is highly
cited?
This paper provided the first convincing experimental evidence of a new
type of s-wave pairing symmetry for the newly discovered iron-based
high temperature superconductors by
observing the Fermi-surface-dependent nodeless superconducting gaps in an
optimally doped pnictide using angle-resolved photoelectron spectroscopy
(ARPES).
Pairing symmetry consists of the momentum information of the amplitude and
phase of the superconducting energy gap, which represents the energy needed
to break the pairs of electrons (Cooper pairs) apart and destroy the
superconductivity along each direction.
Thus, knowing the pairing symmetry is a crucial step in understanding the
superconducting mechanism of a superconductor. In the case of
high-temperature copper-based superconductors, the determination of a
d-wave pairing symmetry is arguably the most important achievement of the
intensive research efforts which have taken place over a period of 23
years.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
ARPES
directly
probes the
superconducting
gap in single
crystals...
This paper describes the discovery of a new class of superconducting gap
which is isotropic along any given Fermi surface, yet varies strongly among
different Fermi surfaces.
Would you summarize the significance of your paper in
layman's terms?
Understanding how a material completely loses its electrical resistance is
of great importance from both the fundamental and applied sides of
superconductors. Electrons in a superconductor form pairs, and lock into a
single phase of motion, similar to the example that many downhill skiers
hold their hands together, and are thus able to overcome small bumps or
resistance along their way.
In a quantum world, a very small resistance is quantized into an absolute
zero resistance. Crucial information of how strong is the binding force for
the pairs and what is the preferred direction of this binding is reflected
from the pairing symmetry of a superconductor.
The surprising discovery of high-temperature superconductivity (as high as
55K) in many iron-based compounds has opened a new route in searching for
new high-performance superconductors, and the understanding of their
pairing symmetry may shine a light on this new direction.
How did you become involved in this research, and were
there any problems along the way?
I have been doing research in understanding novel superconductors over the
past 17 years, and I've made important contributions in measuring the
pairing symmetry and other electronic properties of copper-based
superconductors.
The combination of ultrahigh resolution of ARPES and the high quality of
single crystals has enabled us to clearly observe superconducting energy
gaps and to accurately determine their magnitudes on different Fermi
surfaces in iron-based superconductors. The biggest challenge we
encountered in our experiment was to find a way to prepare clean sample
surfaces for ARPES measurements.
Where do you see your research leading in the
future?
We are continuing to do research towards achieving a full understanding of
the superconducting mechanism of iron-based superconductors, and have made
significant progress since the publication of this paper.
We have accumulated much experimental evidence for inter-Fermi-surface
interactions being a driving force for electron pairing in these
superconductors. Our research on iron-based superconductors may also lead
to a better understanding of copper-based high-temperature superconductors,
since both materials have many of the same properties in common. In the
meantime, we hope that our research in this fundamental area can one day
lead to better applications of superconducting technology.
Hong Ding
Distinguished Professor and Chief Scientist
Institute of Physics
Chinese Academy of Sciences
Beijing, People's Republic of China (PRC)
ARPES directly probes the
superconducting gap in single crystals
Ba0.6K0.4Fe2As2
(
Tc = 37 K).
Two nodeless and nearly isotropic superconducting gaps are observed around
their respective Fermi surface sheets: a large gap (D ~ 12
meV) on the small hole-like and electron-like FS sheets, and a small gap (~
6 meV) on the large hole-like FS. Both gaps close simultaneously at the
bulk Tc (inset).
(Adapted from H. Ding et
al., EPL 83,
47001, 2008.).