Science thomsonreuters.com

My research is focused on correlated electron materials, in which the electrons in a solid are in a strictly localized state, or pinned. An electron can behave like a sort of wave in the solid, but only an electron can stop an electron by their mutual interaction -- their motion is almost freezed out. That is the essence of correlated electron systems. In the case of the copper oxide high-Tc superconductors, the frozen electrons that make an insulator are turned into a metal, and then immediately its state is a high-Tc superconductor. But in another compound, it's sort of a ferromagneticmetal. Of course, the result is quite different, but still the common background is the melting of the electrons within the solid.

It's a sort of alchemy.

With correlated-electron materials my favorite word is 'emergence.' Emergence means many independent components come together to generate surprising outcomes. The entirety of the material's property cannot be described by the sum of the individual components.

I believe correlated electron materials represent an important area of science we need to realize our dreams. Of course, our dreams are not to know the ultimate nature of the universe or such a big thing as that, but we are trying to obtain unconventional electronic functions in solids. In other words, the goal is to develop a new electronics -- not in the narrow sense like semiconductor electronics.

I just read Physics of the Impossible by the U.S. physicist Michio Kaku. I was very impressed by his book, and actually my own goal is to realize the physics of semi-impossible in condensed matter science, which may lead to innovative and even revolutionary technologies.

With this in mind, I have drawn up a list I call "Innovation 4". If certain performance measures could be realized - all including the number 4 -- it would create a revolution in our daily lives through basic discoveries in physics.

In energy transfer, we need 400 Kelvin in order to realize a real room temperature superconductor. At the moment we have 130 or 140 Kelvin superconductors. So we need not only three times the effort to achieve this, but also three times the innovation. High-Tc is a main target of our research.

Another case is thermoelectric materials. Our goal is to produce materials for ultra-low energy consuming electronics. The thermoelectric effect tells us we can generate electricity from temperature differences. An example is the air conditioner, which uses a compressor for refrigeration - that's 19th century thermodynamics.  But if we could directly convert electricity to heat conduction, that would be better. We usually measure this by the so-called thermal figure of merit (ZT). At the moment, ZT is typically 1 or a little more. But if this value exceeds 3 or 4, then every compressor can go away and we can immediately replace it with a direct heat-electricity transformation.

And another case, in terms of energy conversion, is solar cells. As you know, the quantum efficiency is now at 10%, but for industrial use 40% would be very important. I think correlated electron materials could produce a very highly efficient solar cell. This may be 10 years away.

And batteries, too. This is the problem of energy storage. The best performance of the present state-of-the-art batteries is 100 watt-hour per kilogram. If you can increase this performance three or four times, it would make a great difference in our mobile computing society. Our battery technology is classical electrochemistry. So we are thinking there is a chance to move from the classical concept to more advanced quantum technologies with correlated electron materials.

In summary, as you can see, we are only about one-third of the way to our ultimate goal in these areas.

I use the Web of Science everyday. Mainly I use the database to identify new materials or new physical parameters. Actually for me, I want the challenge of working in new fields. I am always trying to work in new fields. I don't know what are the key papers in these new fields. I input some keywords in the database and maybe see thousands of papers, but then I focus on the highly cited papers and perhaps the review papers.

And there is another very good use of the Web of Science: We use it to search for good candidates. It's very, very important. So when we get a lot of proposals or applications for review, we search the database to see what are the candidates' activities or reputation in the field.