Prof. Fumiko Yonezawa, 2005 Laureate for her pioneering theory and computer simulations of amorphous semiconductors and liquid metals
For her pioneering theory and computer simulations of amorphous semiconductors and liquid metals.
Who she is. Fumiko Yonezawa is Professor of Physics at the University of Keio, Yokohama, Japan. Professor Fumiko Yonezawa’s scientific career began in the mid-1960s when, as part of her master’s thesis, she proposed a new method for calculating the electronic density of states in disordered systems. This research field was in its infancy at the time, but has since grown to include the study of non-crystalline solids, amorphous materials, glass, alloys, and liquid metals. In 1968, she was one of four young scientists who, working independently, developed a groundbreaking theory called coherent potential approximation, or CPA, described as “a quiet but radical revolution” that provided a compelling explanation for various physical properties of disordered systems from a theoretical viewpoint. Fumiko Yonezawa, was, from 1995 to 1997, the first woman President of the Physics Society of Japan and is currently an emeritus professor at Keio University.
What she does. Professor Yonezawa’s major projects have focused on topics ranging from non-crystalline materials to computational physics and complex liquids. After earning a PhD in physics from Kyoto University, she was a visiting researcher at Yeshiva University (New York) and the City College of New York from 1972 to 1975. Upon her return to Japan, she founded a scientific society that continues today to have a major impact on research in amorphous semiconductors. Her research has helped elucidate the electronic and optical properties of amorphous semiconductors with an eye to technological applications. She accomplished monumental work in the field of glass transition and, in the 1990s, she and her graduate students earned international recognition for their discovery of a completely new mechanism in metal-nonmetal transition.
As both a researcher and a leader in her field, Dr. Yonezawa has organized many international conferences and symposia. In 1995, she was elected President of the Physical Society of Japan. Of the society’s some 20,000 members, only about 600 (roughly 3 percent) are women. This was the first time a woman had been elected to head the society in its 100-year history.
In Japan, less than one percent of physicists are women. As an internationally esteemed pioneer in this discipline, Fumiko Yonezawa has served as a singular role model for women scientists in her own country and abroad.
Establishing order in disorder. Matter is more or less ordered, and the state of order determines its properties. In a gas, the atoms and molecules are independent, except for occasional collisions. In a liquid, the attraction between atoms is weak so that they are able to move around. In a crystal, the atoms are bonded together in a regular lattice, for example at the corners of cubes piled up like a child’s building blocks (tessellation). In a glass, the atomic constituents are not free to move, but they are disordered as in a liquid that had been instantly frozen.
Ever since her student days, Fumiko Yonezawa has been working on the properties of disordered (or amorphous) systems. She arrived at this rather complicated area of physics on the basis of careful attention to the delicate details of simple ideas – an approach that from a cultural point of view can be regarded as typically Japanese. For a long time, it had been easier to define the amorphous state by specifying what it was not, rather than what it was.
Fumiko Yonezawa felt that disorder was not chaos, and she determined distinctions between various types of microscopic disorders, such as structural disorder, in which the atoms are not in regular positions, and substitutional disorder (as in binary alloys), in which the geometry is identical to that of a well-ordered crystal but where different atoms are randomly placed at regular sites. Professor Yonezawa has put some order in disordered systems – precisely in order to calculate their properties: the approximations made in these different cases have to be adapted, and using some “high-wire” mathematics she was then able to predict certain properties of amorphous or glassy substances such as their conductivity and stability.
The long instability of glass. Glass is always unstable, and over time transfers to the state of perfect crystal, but this change can take an extremely long time. On the windscreens of very old cars you can see – near the edges of the frame – blue and white circular areas where the glass has crystallized. The transformation of the glass into a crystalline form had taken a very long time. Nowadays you don’t see that, firstly because glass-making has improved and secondly because people don’t keep cars that long.
The properties of glasses depend on the speed of the temperature decrease in their manufacturing process, and this dependence has been thoroughly investigated by Fumiko Yonezawa using computer simulations.
In recent decades there has been an interest in liquid metals such as liquid mercury and liquid sodium. Liquid metals are types of liquids whose electrical behaviors are metallic. The advantage of studying liquid metals is that it is possible to evaluate the changes in their physical properties over a wide range of densities. These properties have been calculated by Fumiko Yonezawa using techniques she has been developing throughout her life.
Starting from scratch. In physics, as in many other fields of natural science, research has traditionally been carried out through experiments and theoretical analysis. The advent of inexpensive computing power has created a new trend of computer-assisted physics. The computer simulation of matter has been used extensively by Professor Yonezawa in order to understand how liquids become crystals or amorphous solids. “You take atoms, put them in a box, apply pressure, heat them up, and see what happens,” she says with a smile, “but it’s not easy.” She has obtained a number of results that, except with hindsight, could not have been obtained by other methods. Of course, it is a difficult and new technique, but Fumiko Yonezawa’s various achievements would not have been secured by taking an “easy route”.
Professor Yonezawa is a woman of amazing and almost incredible intellectual voraciousness. She has enormous confidence in the powers of the human mind and thinks of theoretical physics as being like a very hard but enjoyable climb up a mountain – but without either a map or a guide. She therefore decided she had to pioneer a new path by herself.
Originality comes first. “Aim high! Choose the best subject in the field that interests you most – the newest and most different subject you can think of. There are thousands of researchers working in the fashionable fields, so there is no point in joining them. It is a tough race that ends with a great discovery, and only the first person to get there is the winner. It is a case of ‘winner takes all’. So the best strategy is to set out as early as possible towards your goal – before anyone else even realizes that such a goal exists. If at any stage what you are trying to do fails, do not despair. Simply make a fresh start. Think positively and you will always achieve more than you expect to. I have been doing that since I was very young.”
What lies beyond the end of the universe? “My mother loved mathematics and at high school she did so well in geometry that she had the dream of continuing with her studies at the university. But at that time women were not accepted by universities in Japan, and even if they had been my grandfather would not have allowed her to go for fear that she might miss out on the opportunity to get married. In a way I fulfilled my mother’s dream.” “When I was a child, I would keep asking my family all sorts of questions. ‘Why doesn’t the Moon fall on us?’ ‘What is beyond the furthest star?’ ‘Where does the universe end?’ ‘What is beyond the universe?’ I would lie awake at night thinking about the beginning of time. Curiosity is the scientist’s greatest asset.”
Why don’t you try to do both? As a young graduate student, Fumiko Yonezawa had to face the usual handicaps and worries when her boyfriend proposed to her. “My future husband was a student of economics. At that time I saw it as a straight choice: marriage and no physics or physics and no marriage. I thought that way because most of the successful female scientists at the time were unmarried. My husband-to-be reacted as if he was inspired by Marie Curie. He said: ‘Why don’t you try to do both?’ These words changed my philosophy for life: I decided I would take everything I want in life, no matter how difficult it was to do. Marie Curie’s example was proof that it was possible: one could do both.”
The young research scientist’s encounter with the Nobel Laureate Hideki Yukawa was another stroke of luck for her, as he was always very encouraging and supportive. Yukawa had worked alone without colleagues, but even so he had predicted the existence of a particle, the meson, which would be discovered some years later in cosmic rays. Yukawa understood how hard it was to row alone against the tide.
“So I completed my work on disordered systems in 1967, just before I had my second daughter. I felt sure no one had understood disordered systems properly, and so I invented the coherent potential approximation (CPA) for the evaluation of the electronic properties of disordered systems. But I was wrong – to my surprise I found out that the same theory had been invented independently at almost the same time by three young physicists of my age. The theory worked beautifully for explaining various physical properties of disordered systems.”
“I rush back to my desk, shouting “Eureka! Eureka!”
“How do things become clear? In a way the brain seems to identify with the scientist’s subject of study – the transition from disorder to order. “Illumination and inspiration do not come when I am working at my desk. I have to struggle for hours, days and weeks with mathematical equations, formulations and theories – and then when I start cooking or take a bath the idea all of a sudden comes into my mind, and I rush back to my desk shouting ‘Eureka!’ The transition happens unexpectedly, but after a lot of work.”
Build me a Time Machine…
Fumiko Yonezawa has maintained the inquisitiveness of her childhood. She dreams of establishing a grand unified theory covering the four kinds of force existing in the universe, i.e. gravitational force, electromagnetic force, and weak and strong nuclear force. A related question she would like to understand is why – and not only how – the Big Bang happened, what it was like before the Big Bang (if that question means anything), why gravitational and electromagnetic forces vary in inverse proportion to distance…“I should like to ask the genie in the bottle to build me a Time Machine so I can go back into the past and travel to the future to see what it is going to be like. But this is not a scientific dream, because as a physicist I do not think we can make a Time Machine.”
It could not have happened 60 years ago. “Going back in time, one has to admit that, although progress has been slow, the situation for women scientists has been improving: I was elected President of the Physics Society of Japan by male physicists, and that could not have happened 40 years ago, when my mother was not even granted access to university. It is clear that male physicists recognize the scientific achievements of female scientists. My advice to a young person wanting to become a scientist would be: ‘Forget you are a man or a woman, and let the revolution inside you lead the way.”
“However, the main reason there are still so few young girls going into science is that it is rather difficult to find models of women scientists. If a woman is a singer or a painter or a writer, everyone can find and enjoy her songs, her paintings or her novels. But the achievements of a woman scientist are for the most part presented in scientific papers which are not so accessible to a lay person. This is why I really appreciate the fact that the L’ORÉAL-UNESCO awards are given to women scientists and made public to everybody, and not just to scientists.”