Aiming at a BreakthroughPresent Views and Future Prospectsof Superconductivity Scienceand Technology
Kohji Kishio
Chief, Superconductivity Division

Since first being discovered in 1911, superconductivity has been
regarded and classified as one of the most puzzling and fascinating
phenomena in low temperature physics. However, the critical temperature (Tc) of superconductivity in any known materials remained below
23 K for a very long time. A famous 1957 paper by Bardeen, Cooper and Schrieffer ( BCS ) successfully explained the superconductivity
mechanism but predicted a theoretical Tc limit of only below 30 K.
In 1986, Bednorz and Mülller in Switzerland suggested the possible existence of superconductivity with Tc as high as 30 K in a cuprate (copper oxide), La-Ba-Cu-O. Its reproducibility was immediately
confirmed by S. Uchida et al.(Tokyo) and was reported in the firstpage of the Letters section of Vol. 26 of JJAP, (Jpn. J. Appl. Phys.,
26 L1, (1987)). Encouraged by this report, superconductivity withan incredibly high Tc level of over 90 K was found in Y-Ba-Cu-O in
the USA within a few weeks. Early the following year, H. Maeda etal.(Tsukuba) reached the milestone of Tc of over 110 K for the firsttime in Bi-Sr-Ca-Cu-O compounds ( JJAP, 27 L209, (1988) ).
It should be emphasized that these historically important papers
were both published in JJAP, and that they triggered the worldwide“HTSC” fever. This was certainly one of the great technical breakthroughs in the history of both fundamental and applied physics .
Since then, JSAP (the Japan Society of Applied Physics) has madenumerous and significant contributions to the field. The Superconductivity Division was officially established in 1990 and since then its
nearly 350 members have continued to do important work on various

Machinery

MedicalMRI
MCGTransportation
SC propShip

Mag lev
Train

Magnetic
BearingIndustrial
MagnetMotor

MEG

Big ScienceSpaceScience

SOR

Electriccar

Electronics & IT

Magnetic
ShieldAccelerator
Elevator

SQUID

Mobile
Com

Power
Cable

FusionReactorEnergy, Power
SMES

Josephson
ComputerDigital
DeviceAnalogue
DeviceCurrent
LeadSC
Generator

Superconductivity

Chemistry

Physics

Engineering

activities. These include planning general
symposia and specific-subject-oriented research meetings, publishing “Superconductivity News”, and writing and editing reviews and research articles in
the monthly-issued (in Japanese) “Oyo Buturi” journal .
The main and final goal of our division is the application of superconductivity in various scientific and technological fields in thevery near future. Figure 1 illustrates expected practical future technologies in the form of an “Application Tree”. They cover a vast
range of areas, including the electronics, transportation, medicine,machinery, and energy-power fields. Some applications are presently
in wide use based on low Tc superconductors, e.g., strong magnets
for magnetic resonance imaging (MRI), industrial material processing,laboratory research and big accelerators. On the other hand, HTSCbased current leads, microwave devices, SQUID, etc. are now alsoavailable in commercial devices. The practical application of HTSC
materials is extremely attractive since it makes the use of very lowcost liquid nitrogen possible as a coolant.
Many types of cryo-coolers are also now available down to 4.2K
in medium-scale applications. For small-scale thin-film devices suchas microwave application, electronic cooling devices may be used infuture down to 77 K. These coolers can be operated without any liquid coolants such as helium or nitrogen.
The above-mentioned scope does not exclude our efforts in understanding fundamental physical aspects. In HTSC materials, there
are many superconductivity mechanism details that still remain unclear, in contrast to the phonon-mediated scenario in the originalBCS. The pairing symmetry of Cooper pairs, probably d-wave inHTSC, and the extremely short coherence length (~ 1 nm), poses bighurdles in the designing and practical fabrication of both electronicand power devices. As a brief example, electrical power cables ormagnetic coils of lengths much longer than 1km must be continuously fabricated, while their microstrucures such as grain boundary thickness and flux-pinning centers have to be controlled with nm-scaleprecision. Within the context of multi-component and complicatedstructural materials, this poses a big challenge in the field of nm-scalechemistry.
Figure 1 illustrates how basic roots such as physics, chemistry
and engineering need to be applied to superconductivity applications.
The superconductivity being a truly multi- and trans-disciplinary field,
we foresee other big breakthroughs in the very near future with continuous help from various science and technology communities.

Fig.1 Application Tree of Superconductivity

JSAP International No.6 (July 2002)

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