Tony Ford (MSF Secretariat)

Preface

Professor Maki Kawai Chair, MSF Steering Committee Director General, Institute for Molecular Science Professor Emeritus of the University of Tokyo

Cultivating new horizons for Condensed Matter Science

The Millennium Science Forum (MSF) was established based on the voices of senior scientists who lead the modern research with the intention of cultivating new horizons for Condensed Matter Science.

On this occasion of 20 years of the MSF, we would like to show the how the mission of the MSF was conceived and what was attained by twenty-two talented prize winners. The start was in 1998, when Professors Noboru Miura, Hidetoshi Fukuyama, the late Koichi Kitazawa and Sir Peter Williams met in Tokyo and came up with the idea of the MSF which was started in the following year, 1999. The Sir Martin Wood Prize was set as the core program of the MSF and Mr. Yasunobu Nakamura of NTT, currently Professor of the University of Tokyo, became the 1st awardee. In November 2018, the twentieth Sir Martin Wood Prize will be awarded to Associate Professor Yoshihiko Okamoto of Nagoya University.

Here we showcase twenty-two Prize Winners with their achievements and their development since the MSF was founded. Successful advancement in their personal careers indicates the promotion of Condensed Matter Science and individual descriptions of their research represents the development of Condensed Matter Science itself in two decades. We are confident that you will enjoy the new era of the field. Sir Martin Wood Prize winners are given the opportunity of lecture trips to UK universities and institutes in Germany. This is a noteworthy experience that ties together young generations of Japan and the UK.

The MSF has been always been kindly supported by the British Embassy in Tokyo, and also by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. We are grateful to Mr. Paul Madden, British Ambassador to Japan, and to Mr. Touichi Sakata, former vice minister of MEXT, for their contribution of warm words to this book.

Last but not least, twenty years of the MSF would not be possible without the devotion of Oxford Instrument KK. Without the encouragement by Mr. Jiro Kitaura, former president, the MSF would not have existed. The steering committee of the MSF is grateful for Oxford Instruments’ continued support over the past twenty years and for the future.

20 years of the Millennium Science Forum 3

Contents

Page Preface 3 Professor Maki Kawai (Chair, Millennium Science Forum Steering Committee)

Founder’s Message 6 Professor Noboru Miura (Founder, Millennium Science Forum)

Greetings Sir Martin Wood (Founder, Oxford Instruments) 8 Sir Peter Williams (Member of Millennium Science Forum Steering Committee 10 Former Chairman, Oxford Instruments) Professor Robin Nicholas (University of Oxford) 12 Mr. Paul Madden (British Ambassador to Japan) 14 Mr. Touichi Sakata (Former vice minister, MEXT) 16

Introduction to the Sir Martin Wood Prize Professor Hidetoshi Fukuyama (Chair, Sir Martin Wood Prize Selection Committee) 18 Locations of Sir Martin Wood Prize Lectures 19 Lecture Trip Memories 20

Brief History of the MSF 22 Tony Ford (MSF Secretariat)

Messages from the Sir Martin Wood Prize Winners 25 List of the Winners in alphabetical order 70

Appendix Prize Ceremony Memories 72 Record of the MSF Steering Committee and Selection Committee members 76 Guest Speakers at the Millennium Science Forum 77

20 years of the Millennium Science Forum 5 Founder’s Message

Professor Noboru Miura Founder, Millennium Science Forum Professor Emeritus of the University of Tokyo

“How can we contribute to building a bridge between the science communities of Japan and the UK by promoting the activities of top young researchers, rather than simply doing business in Japan?” “Can we search for a scheme together?”

In 1997 Mr. Kitaura of Oxford Instruments asked me these unexpected, and at the same time, difficult questions so I consulted with Professor Koichi Kitazawa and Professor Hidetoshi Fukuyama. I was familiar with various cases of joint programmes between academia and industry that in many cases had glorious start-ups, but unfortunately did not last. I noticed a variety of reasons for such programmes being unsustainable so I was mindful that we needed to discuss in detail to reach a common understanding. Our concerns disappeared when we talked further with Mr. Kitaura and he assured us that Oxford Instruments direction will be different to the “unsuccessful examples” we had seen in the past and he told us:- “We just want to bridge the science communities of Japan and the UK by encouraging young scientists without linkage to the Oxford Instruments business, hence the scheme will not have the company name associated with it” This was the first time we had heard of a programme that did not have the name of the sponsor or some specific promotional target combined with it, so we immediately decided to support the activity and quickly moved ahead to create the whole scheme. At this stage I received strong encouragement from the Oxford Instruments Chairman, Sir Peter Williams, to lead the initiative with Oxford Instruments Japan. The next difficult question we faced was naming and identifying the mission and spirit of

6 20 years of the Millennium Science Forum 20 years of the Millennium Science Forum

the activity. After some discussions we decided to call it the “Millennium Science Forum” (MSF) with a vision of “Looking to the Future” with commitment, consistency and continuity. At the same time we decided that the MSF should have a core program to give awards to young researchers. I was happy that Sir Martin Wood, Founder of Oxford Instruments, kindly agreed to call the award the “Sir Martin Wood Prize” and we asked our academic colleagues to support and become involved with the prize. Based on these fundamental points, everything has run smoothly since then.

In 1999, we were greatly honored that HRH The Princess Royal and many distinguished guests attended the inaugural event at The British Embassy in Tokyo. The MSF has now been recognized by the scientific communities in both Japan and the UK. Below is the charter adopted for the MSF upon which our entire activities are based on and gives us strong encouragement to continue. 1. Oxford Instruments name is not directly associated with the MSF however following the will of the founder of the company, and to motivate people externally and internally, the name of the award is the “Sir Martin Wood Prize” 2. From the outset the emphasis will be on excellent results to maintain the activities, including management structure of the MSF. 3. Through these activities, our objective is to build bridges between the scientific communities of Japan and the UK.

I strongly hope that by keeping our original concept the MSF will continue to prosper through the constant adoption of innovative ideas and design.

20 years of the Millennium Science Forum 7 Greetings

Sir Martin Wood Founder, Oxford Instruments

It was in 1955 that I first started working with physicists carrying out research in aspects of Condensed Matter Physics – then known as Solid State Physics. I was working under Dr. Nicholas Kurti at the University of Oxford's Clarendon laboratory, managing the High Magnetic Field facility, and developing new types of resistive magnet and research equipment for their experiments.

Other universities wanted similar equipment so, in 1959, with the help of my wife, Audrey, I started the Oxford Instruments Company. This was two years before the American breakthrough in superconductivity which resulted in useable superconductors for magnets. It led to a great expansion of research in the field, and rapid growth at Oxford Instruments.

Condensed Matter Physics has come a long way since then. I am full of admiration for the research work and achievements of the scientists who have won this Prize, which they have outlined in this booklet. I am very happy to have met many of the prize- winners in Tokyo, and most of them in my house in Oxfordshire.

8 20 years of the Millennium Science Forum I would like to thank the eminent scientists in the Millennium Science Forum who have given their time to reading all the submitted papers and judging between them. Especial thanks must go to Professor Noboru Miura, who I have known for many years and who was the first chairman of this committee. He has worked tirelessly and has accompanied most of the prize-winners on their lecture tours in the UK. Many thanks also to Tony Ford, who first developed this project with Professor Miura, and has organised the presentations and the lecture tours from the beginning.

I hope the prize will continue to encourage and reward young scientists in this field for many years to come.

20 years of the Millennium Science Forum 9 Sir Peter Williams Member of Millennium Science Forum Steering Committee Former Chairman, Oxford Instruments

During 1998, a small group of British and Japanese scientists and technologists gathered in the City Club of Tokyo, in Akasaka, to discuss how to mark the forthcoming millennium celebrations. Convened by Jiro Kitaura, then-president of Oxford Instruments KK, the group hatched a plan under his leadership to hold an annual seminar, if possible at the British Embassy, Tokyo, to showcase cutting edge developments in Japan in condensed matter physics. The Millennium Science Forum was born.

Those present—Professor Noboru Miura, Professor Hidetoshi Fukuyama, the late Professor Koichi Kitazawa and I—further proposed to mark the occasion each year with the award of a prize to a young Japanese scientist, who would subsequently visit the UK to give prestige lectures at the University of Oxford and other leading universities. This plan has since been extended to include German research institutions.

By chance, in March 1999, the planned announcement of the MSF at the British Embassy, Tokyo coincided with a visit to Japan by Her Royal Highness Princess Anne, the Princess Royal, to attend a meeting of the International Olympic Committee, of which she is a member. She enthusiastically agreed to join me and Sir David Wright GCMG LVO, then HM Ambassador, at the ceremony. Thus, the MSF enjoyed a royal opening.

10 20 years of the Millennium Science Forum The Princess Royal’s good wishes at the launch of the MSF have undoubtedly borne fruit. The alumni list of winners of the Sir Martin Wood Prize comprises emerging leaders in their fields in Japan, with increasingly global reputations. The 20th such prize will be awarded in 2018.

The UK and Japan have always enjoyed close partnerships in science, and the exchange of visits and ideas between young scientists in our two nations both strengthens and deepens this bond. In years to come, as the prize winners rise in prominence in their respective fields, the enhancement in mutual understanding between the scientific leaders of the UK and Japan will have a significance and importance well beyond the sphere of science. Today, in a world filled with uncertainties, these relationships constitute a precious asset.

On behalf of all my colleagues in the MSF, may I in conclusion thank HM Ambassador Paul Madden CMG for his continuing support; we are indebted to him and his predecessors over the past 20 years for their invaluable and positive contribution.

20 years of the Millennium Science Forum 11 Professor Robin Nicholas Member of Millennium Science Forum Steering Committee University of Oxford

It is a great pleasure to contribute to this celebration of 20 years of the Millennium Science Forum and the Sir Martin Wood Prize. As with many important institutions the origins of the foundation lie in the close personal interactions developed by individuals, in particular Professor Noboru Miura and Sir Martin Wood. Noboru first came to the UK as a relatively young visitor in his early thirties to work in the University of Oxford in the research group of Professor Tony Stradling on the properties of semiconductors in high magnetic fields, in the laboratory first set up by Sir Martin together with Professor Nicholas Kurti. This proved to be a formative experience leading to a lifelong series of collaborations and interactions with UK scientists. About ten years later a young Japanese graduate student studying at the University of Oxford walked into the garden of Sir Martin Wood, which he had opened to the public for a few days. Sir Martin’s garden is on the banks of the Thames, which the student was studying as a historically important transport route. The student told Sir Martin that he lived in the ‘middle’ of Tokyo and they struck up an immediate friendship. Within a few years the student had become Crown Prince Naruhito and the two have remained good friends ever since. Both Noboru and Sir Martin were convinced of the great benefits of intellectual and cultural exchange at an early career stage, so they persuaded Oxford Instruments to help fund the Millennium Science Forum to promote this exchange and to give it a clear scientific focus in the area of condensed matter physics which had been vital to both of them and to the business of Oxford Instruments in both the UK and Japan.

12 20 years of the Millennium Science Forum To achieve this they set up the prize with: The winner to be a person under 40, having performed research in a Japanese institute, selected by a committee of distinguished Japanese scientists headed for many years by Professor Noboru Miura, Institute of Solid State Physics, Tokyo and now by Professor Hidetoshi Fukuyama, Tokyo University of Science. The prize awarded being ¥500,000 and the opportunity to lecture at UK & EU Universities. The prize has been instrumental in promoting the careers of many of the prize-winners through its special formulation of a lecture tour to prestigious Universities mainly in the UK, combined with a prize winning presentation in the UK embassy in Tokyo with special guest lecturers and an audience of many of the top scientists in Japan, hosted by the British Ambassador. Speaking personally, having attended the lectures from all of the prize winners, presented in the Sir Martin Wood lecture theatre in Oxford, I never cease to be impressed by the imagination, skill and academic excellence of the science which they have done in Japan. The elements of cultural exchange have not been forgotten either. As Professor Yasunobu Nakamura, the first prize winner, says in his message his visit was also the first time that he was introduced to another British phenomenon, Harry Potter! On a final note I would also like to give special thanks to Tony Ford, who has been unstinting in his efforts to ensure the smooth running of the prize and to ensure that both the prize winners and the UK institutions have benefited enormously from their lecture tours.

20 years of the Millennium Science Forum 13 Mr. Paul Madden British Ambassador to Japan

I am delighted to congratulate the Millennium Science Forum on the 20th anniversary of the Sir Martin Wood Prize. The Prize has been very successful in motivating young researchers in their quest to further the understanding of the fundamental properties of materials and matter.

Japan and the UK are strongly committed to science and innovation. Both countries have a long history of making significant contributions to scientific understanding and improving the lives of people around the world. Collaborations between scientists are of vital importance in the extensive relationship between the two countries. The Sir Martin Wood Prize allows international relationships to be formed in the early stage of a scientist’s careers. I am sure that the experience of the winners visiting UK Universities and research institutes provides them with inspiration for new ideas for their research.

The prize selection committee has an excellent record of choosing recipients of the Sir Martin Wood Prize who have performed world class research. Leading UK scientists recognize the value of the prize and are always keen to host the Sir Martin Wood Lectures. I am also grateful to Oxford Instruments and Sir Martin Wood for establishing and sustaining the Millennium Science Forum and Sir Martin Wood Prize

14 20 years of the Millennium Science Forum for so many years. It is important that both Japan and the UK continue to cultivate long term partnerships between the academic and industrial research communities in our two countries.

In addition to the scientific discussions the prize winners have in the UK, they are also able to gain insights and understanding of the culture and heritage of the UK that will benefit their future collaborations and relationships with their counterparts. I hope that the Sir Martin Wood Prize will continue to motivate young Japanese scientists to initiate innovative research and collaborate with UK researchers.

I wish the Sir Martin Wood Prize every success for the future.

20 years of the Millennium Science Forum 15 Mr. Touichi Sakata President of the Japan Space Forum Former Vice Minister of the Ministry of Education, Culture, Sports, Science and Technology

Congratulations on the 20th anniversary of the establishment of the Millennium Science Forum!

The Millennium Science Forum (MSF), which was established to foster the exchange of science and technology between Japan and the UK, was founded in March 1999. In 2018 it will award the 20th Sir Martin Wood Prize. Given that I have participated in the Japanese government for the promotion of scientific research, I sincerely congratulate the MSF on its 20th anniversary. I would like to express my deep gratitude and respect to British physicist Sir Peter Williams and Professor Emeritus Noboru Miura of the University of Tokyo who dedicated themselves to founding the MSF. My sincere thanks, too, to all the other individuals in Japan and the UK who have been involved in the foundation and operation of the MSF.

In Japan at present, contributing to the realisation of innovation using outcomes from scientific research is considered crucial. Research on advanced materials science based on physics and chemistry is one of the important fields of research that will pave the way to innovation, including the development of revolutionary devices. The MSF’s decision to promote condensed matter science is one response to these developments.

16 20 years of the Millennium Science Forum I applaud the establishment of the Sir Martin Wood Prize that is awarded by the MSF each year, to a young condensed matter scientist working in Japan.

I participated in the MSF on 4 occasions, each time I attended the Sir Martin Wood Prize ceremony, which is held annually in the British Embassy, Tokyo, I noticed a wide range of researchers from both Japan and the UK. I also noticed that the MSF contributes greatly to promoting intimate science and technology exchanges between both countries. Both Japan and the UK are island countries, but they promote science and technology to, and support exchanges with, other parts of the world. As we share such goals, we have been able to deepen our bilateral science and technology exchanges through the MSF over the past 20 years. These exchanges have undoubtedly contributed to the development and strengthening of friendship between our two countries.

I believe that the MSF will continue to offer exchange opportunities to researchers based in Japan and the UK beyond its 20th anniversary. I also hope that past and future recipients of the Sir Martin Wood Prize will play active roles in the development of science worldwide.

20 years of the Millennium Science Forum 17 Introduction to the Sir Martin Wood Prize

Professor Hidetoshi Fukuyama Chair, Sir Martin Wood Prize Selection Committee Adviser to the Chair and the President, Tokyo University of Science Professor Emeritus, the University of Tokyo

The Sir Martin Wood Prize was established in the first committee meeting of the Millennium Science Forum (MSF), on 23rd January 1999 at Oxford Instruments KK, after preliminary discussions on 23rd July 1998 and 11th October 1998. Jiro Kitaura, then-president of Oxford Instruments KK, had expressed with vigour his strong vision for progress in science and technology. He described the mission of the MSF as follows: • To promote science in the 21st century by increasing the opportunity of discussion among scientists • To promote scientific exchange between the UK and Japan • To award prizes to young scientists

This mission of the MSF remains unchanged. Its award for young scientists was naturally named the Sir Martin Wood Prize, which was suggested by Professor Koichi Kitazawa in the second preliminary meeting. To be eligible for the prize, applicants must: • Specialise in condensed matter science • Perform their research in a Japanese university or institute • Be under 40 years of age in the year of their application; any nationality may apply

Besides a financial award of ¥500,000, the Sir Martin Wood Prize has a unique feature: the recipient has the opportunity to lecture at universities in the UK and European Union, which stimulates and helps every recipient to step up onto the international stage. This special arrangement reflects the nature of the sponsor, Oxford Instruments KK, bridging Japan and UK-EU, and the vision thereof. The Millennium Science Forum was first held on 9th March 1999, in the New Hall of the British Embassy, Tokyo as a ceremonial activity. HRH The Princess Royal delivered greetings and gave an Honorary award to Professor Hiroshi Yasuoka, former director of the Institute of Solid State Physics, the University of Tokyo. Following the presentation of the award Professor Noboru Miura described the Millennium Science Forum’s mission and an introduction letter from Sir Martin Wood was read by Oxford Instruments’ Jiro Kitaura.

18 20 years of the Millennium Science Forum The first Sir Martin Wood Prize was awarded to Yasunobu Nakamura on 17th November 1999, in the same place.

The status of any prize depends on the committee that chooses its winners. The members of the Sir Martin Wood Prize’s selection committee to date are listed in the appendix. Quite often another board, for example an honorary board, sits above the selection committee, but that is not the case for the Sir Martin Wood Prize, reflecting the strong wish of Oxford Instruments, which is again very rare. Because of the high-level scientific activities of each member of the selection committee, every selection meeting has been a very lively occasion for experts to exchange opinions frankly. It is an occasion for the committee to appeal or learn new developments in condensed matter science. To date, the Sir Martin Wood Prize has been awarded to 22 recipients, who in total gave 82 lectures as shown in the Figure below, not only in the UK but also in Germany—an initiative that started in 2015. In 2007, the steering committee was created from the selection committee, for the effective management of the Millennium Science Forum aside from the selection of the Sir Martin Wood Prize recipient.

Locations of Sir Martin Wood Prize Lectures

Sir Martin Wood Prize lectures 2000 to 2018 (82 in total)

Glasgow (1) Lancaster (1) Max Planck Institute, Stuttgart (4) Manchester (6) Leeds (2) Daresbury (1) York (5) Liverpool (1) Sheffield2 ( ) Warwick (2) Nottingham (4) Oxford (19) Cambridge (14) Bristol (2) Royal Holloway (1) Cardiff 1( ) UCL (10) Southampton (2) Royal Society (1) Exeter (1) Imperial College (1) Surrey (1)

20 years of the Millennium Science Forum 19 Lecture Trip Memories

Professor Shirahama at Royal Holloway with Pro- Professor Kimura at Sir Martin’s home with Mrs. fessor Miura and Professor Michael Lea (2002) Miura (2006)

Professor Ohtomo in Cambridge with Professor Professor Saitoh and Professor Ono visit Sir Mar- Fukuyama (2008) tin & Audrey Wood's home (2009)

Professor Hayashi visiting Sir Martin (2015) Professor Kim visiting Liverpool University (2010)

Professor Satoh with Professor Takagi at the Max Sir Martin showing Professor Shibata where Ox- Planck Institute (2016) ford Instruments started (2014)

20 20 years of the Millennium Science Forum Professor Suenaga with his wife and Professor Professor Ohtomo in Oxford with Professors Miura, Kawai in Cambridge (2007) Fukuyama, Briggs and Mr. Matsuura Science At- taché from the Japanese Embassy in London (2008)

Dr. Kim at Sir Martin’s home (2010) Professor Murakami with Professor Eaves in Not- tingham (2011)

Professor Chiba visiting Newton’s birthplace with Professor Ishizaki with Sir Martin and Audrey Professor Miura (2013) Wood (2017)

Professor Robin Nicholas welcoming Professor Professor Yamamoto meeting Sir Martin and Yamamoto to Oxford (2018) Audrey Wood (2018)

20 years of the Millennium Science Forum 21 Brief History of the MSF

Tony Ford MSF Secretariat

Professor Noboru Miura and Sir Martin Wood are the two prominent figures instrumental in the success of the Millennium Science Forum. Sir Martin had just retired as deputy chairman of Oxford Instruments after 41 years’ service when the MSF started in 1999, he readily agreed for the prize to be in his name and welcomed the opportunity to remain involved with the company in a role where he could meet customers and follow technological trends. Professor Noboru Miura was a post-doctoral researcher in the University of Oxford in 1972 when he first met Sir Martin and was happy to rekindle his friendship through the MSF which matched their mutual enthusiasm to motivate researchers to expand international collaborations. Professor Miura’s contribution in increasing UK Japan scientific exchange was recognized by the UK Government and in 2006 he was awarded an OBE (Order of the British Empire). Similarly Sir Martin was awarded The Order of the Rising Sun, Gold Rays with Neck Ribbon by the Japanese government in 2008.

The opportunity for the Sir Martin Wood Prize winners to visit the UK and meet their counterparts with expertise and research interests in the same area of physics, allows the winners to have detailed technical discussions as well as exchanging views on research funding, equipment specifications and in several cases, start new collaborations or aug- ment existing arrangements.

We arrange for the prize winners to visit one of Oxford Instruments’ facilities and show them firsthand how equipment is designed and manufactured. When appropriate we also discuss specific requirements and features for new equipment. Almost all the winners have visited Sir Martin and Audrey Wood at their home in Little Wittenham where they are always given a warm welcome. Sir Martin takes great pride in walking round his garden with the winners and talking about the history of Oxford Instruments by showing some of the devices made by the company in the early days.

22 20 years of the Millennium Science Forum The lectures are normally in the early summer at 4 or 5 venues arranged between Mon- day and Friday. In addition to the academic programme, when time permits we arrange visits to places that have historical or cultural importance to foster greater understanding of the UK. Prize winners have visited Isaac Newton’s birthplace, Green’s windmill; home of theoretician George Green, they have seen James Clerk Maxwell’s original desk and Einstein’s script preserved on a blackboard he used for a lecture. In some cases winners are able to return to the UK and spend more time with their counterparts in Universities they visited on the lecture tour or even visit for a vacation and have a more leisurely time. The MSF is now endorsed by 17 academic societies and organizations. We have been very fortunate to have strong support from the British Embassy in Tokyo from the start and from 2007 the Japanese Embassy in the UK has endorsed the Sir Martin Wood Prize lectures with an initiative started by the then Science Attaché, Mr. Shigekazu Matsuura. Since then a senior representative from the Japanese Embassy in London joins one of the UK lectures and makes a brief address to the audience on the importance of Japan UK scientific collaborations. From 2015, thanks to the generous support of Professor Hidenori Takagi, we have been able to extend the lecture tour to include the Max Planck Institute in Stuttgart.

It is always very pleasing to see prize winners from previous years attending the prize ceremony at the Millennium Science Forum to welcome the new winner to their alumni and give advice on how to structure their lectures for UK audiences.

On a personal note, it is a tremendous pleasure to accompany the prize winners on their lecture visits and inspiring to hear their passion to make discoveries and increase their understanding in their area of expertise. Chatting with the winners informally on a wide range of subjects is always enjoyable and makes me realize that in addition to the winners excel- ling academically, they are all very warm hearted individuals who always bring out the best in those around them. Additionally all the committee members have devoted large amounts of their personal time to MSF activities that have contributed to the success over the past two decades. As a result of the distinguished personal standing of the committee members and prize winners, the MSF has strengthened UK Japan collaboration in scientific research and research based industry and is a successful illustration of “Science Diplomacy”.

I would like to pay tribute to the many other people, including colleagues in Oxford Instruments, who have contributed to the success of the MSF since its inception. In particular we should express gratitude to the Chief Executive of the company who has the foresight to recognize the importance of having strong connections with leading edge researchers in Japan. Hidemi Kurosawa deserves a special mention for her enthusiasm and meticulous planning that ensures the prize selection process and MSF events always pro- ceed smoothly.

20 years of the Millennium Science Forum 23 24 20 years of the Millennium Science Forum Messages from the Sir Martin Wood Prize Winners

Page Yasunobu Nakamura 1st 1999 26 Tokushi Kizuka Joint 2nd 2000 28 Katsuya Shimizu Joint 2nd 2000 30 Keiya Shirahama 3rd 2001 32 Ichiro Terasaki 4th 2002 34 Toshimasa Fujisawa 5th 2003 36 Yuzo Ohno 6th 2004 38 Tsuyoshi Kimura 7th 2005 40 Kazutomo Suenaga 8th 2006 42 Akira Ohtomo 9th 2007 44 Teruo Ono Joint 10th 2008 46 Eiji Saitoh Joint 10th 2008 48 Yousoo Kim 11th 2009 50 Shuichi Murakami 12th 2010 52 Yukio Kawano 13th 2011 54 Daichi Chiba 14th 2012 56 Naoya Shibata 15th 2013 58 Masamitsu Hayashi 16th 2014 60 Takuya Satoh 17th 2015 62 Akihito Ishizaki 18th 2016 64 Michihisa Yamamoto 19th 2017 66 Yoshihiko Okamoto 20th 2018 68

20 years of the Millennium Science Forum 25 Winner in 1999

Current title and affiliation Professor, Research Center for Advanced Science Yasunobu Nakamura and Technology, The University of Tokyo, Team Leader, Center for Emergent Matter Science, RIKEN

1990: B.S., Department of Applied Physics, The University of Tokyo 1992: M.S., Superconductivity Research Course, The University of Tokyo 1992-2011: Researcher, Senior Researcher, Principal Researcher, Research Fellow, NEC Corporation 2001: Visiting Researcher, Department of Applied Physics, Delft University of Technology (Netherlands) 2002-2013: Researcher, RIKEN 2011: D. Eng., Department of Applied Physics, The University of Tokyo 2012-present: Professor, Research Center for Advanced Science and Technology, The University of Tokyo 2014-present: Team Leader, Center for Emergent Matter Science, RIKEN

Quantum coherence in a single Cooper pair box Title and affiliation when prize awarded Senior Researcher, NEC Fundamental Research Laboratories

As a next step, we decided to do a time-domain ex- Abstract when prize awarded periment to demonstrate quantum state control of We demonstrated quantum coherence in a single the charge-number superposition. That was also the Cooper pair box in 1999, which was the first reali- time when ideas of quantum information processing sation of a superconducting qubit as well as a sol- and quantum computing started to spread around the id-state qubit. community. We needed to develop a few new experimental techniques, such as the ultrafast gate-voltage We started our research on single electron transistors pulses for the control and the time-ensemble current in 1992. As the devices were made of aluminium, measurement for the readout, but finally succeeded they became superconductive at low temperatures to observe coherent oscillations (Figure 1) between below 1K. Naturally, we became interested in charge number states, in autumn 1998. The paper Cooper pair tunnelling in those devices and studied was published in Nature, in April 1999. It was well the parity effect, which discriminates the even-odd accepted and triggered research on solid-state quan- parity of the number of electrons in an electrode, as tum computing. well as photon-assisted Cooper pair tunnelling under microwave irradiation around 1995-1996.

During that time, we learned the concept of macroscopic quantum coherence, coined by Tony Leggett in 1980, and the following experimental challenges using SQUID circuits. Macroscopic quantum tunnelling was demonstrated in the 1980s. However, coherence and superposition in macroscopic systems had been elusive. Fig.1 Coherent oscillations observed in the first Cooper pair box experiment. This led us to an experiment of quantum superposition between two distinct charge number states in Progress in Research the Cooper pair box device. In 1997, we published Progress in the field of quantum information science a paper in Phys. Rev. Lett. on the observation of the has been much more rapid than what we expected in energy-level anti-crossing as evidence of the super- 1999. Superconducting quantum circuit technology position. The result was obtained in photon-assisted is one of the most advanced subjects in the field. The tunnelling spectroscopy. coherence time of superconducting qubits, initially about 1 ns and desperately short, has improved by

26 20 years of the Millennium Science Forum five orders of magnitude and is now beyond 100 μs. membrane. More recently, we combined a supercon- On the way, we have learned a lot about physics and ducting qubit and a surface-acoustic-wave (SAW) about engineering of superconducting quantum cir- resonator and strongly coupled microwave photons cuits. The knowledge accumulated collaboratively and SAW phonons. We are also interested in cou- in the community is enormous and still growing, and pling those collective excitations to optical photons more and more groups are working in the field. in order to build a quantum interface between microwave and optical quantum information media. Recently, big corporations, such as Google, IBM Our latest focus is on the development of integrat- and Intel have been developing superconducting ed superconducting qubits and the implementation quantum computers with tens of qubits. Who could of quantum information processing. We are aiming have imagined 20 years ago that everyone would be at scalable architecture allowing for at least a hun- able to use quantum computers on the cloud service? dred qubits. High-fidelity control and readout of the While problems still need to be overcome before qubits are demanded. quantum computers become useful for our society, human beings’ construction and control of such Reflections complex artificial quantum systems is amazing. I would like to express my sincere gratitude and congratulations on the 20th anniversary of the Sir I have been working continuously in the research Martin Wood Prize. It has significantly influenced field since the beginning of my career. After the de- and contributed to the promotion of the research in velopment of the charge qubit in NEC, I spent a year condensed matter physics in Japan. The breadth and (2001-02) as a visiting scientist at Delft University depth of the themes covered by the Sir Martin Wood of Technology, in the Netherlands, where we demon- Prize in the last two decades represent the progress strated a flux qubit, in which a superposition of two of the research fields. It was my greatest honour to flux states was controlled. Around 2004, the phys- be the first prize winner, especially considering the ics of superconducting qubits evolved into the era excellence of the winners who followed me. of circuit quantum electrodynamics (circuit QED) It has been almost 20 years since I received the prize through the happy marriage with quantum optics. from Sir Martin Wood, in 1999. Nevertheless, I viv- Circuit QED turned out to be a powerful tool both idly remember the ceremony at the British Embassy, for fundamental studies and for quantum computing Tokyo as well as my visit to Sir Martin’s manor architectures using superconducting circuits in the house in Oxford. It was my first visit to the UK, microwave domain. Following successful experi- which I enjoyed very much thanks to the kind sup- ments with qubits coupled to a resonator, we also port of Professor Noboru Miura and Tony Ford. My initiated waveguide QED, where qubits are coupled visit to the factory of Oxford Instruments, in Tubney to a 1D transmission line as simple realisations of Wood, was also very exciting. tailored open quantum systems. Now, in microwave During my stay in Oxford, I bought the first volume quantum optics, we can generate and detect single of the Harry Potter series. After 20 years, no one is microwave photons and other non-classical states. surprised by moving pictures on the wall any more. After I moved to The University of Tokyo and start- The evolution of science and technology is so fast. ed a new research group, we began exploring a new Lack of imagination may be the only reason for im- research direction of hybrid quantum systems. We possibility, while the future is not ours to see, Que used superconducting qubits as a tool for quantum Sera, Sera. control and measurement in other physical systems, particularly collective excitations in solid state. For Lecture Trip example, in quantum magnonics, we demonstrated University of Oxford, University of Cambridge, University of Bristol control and measurement of single magnons in a millimetre-scale sphere of ferromagnetic crystal. In quantum nanomechanics, we achieved ground-state Contact Information [email protected] cooling of a vibration mode of a millimetre-scale

20 years of the Millennium Science Forum 27 Winner in 2000

Current title and affiliation Professor, Department of Materials Science, Tokushi Kizuka University of Tsukuba

1991: D.Eng. The University of Tokyo 1991-2002: Associate Professor/Lecturer, School of Engineering, Nagoya University 1998-2001: Researcher, Japan Science and Technology Corporation, Precursory Research for Embryonic Science and Technology 2002: Associate Professor, Institute of Materials Science, University of Tsukuba. 1998-2001: Researcher, Japan Science and Technology Agency, Precursory Research for Embryonic Science and Technology (Advanced Type) 2010-present: Professor, Department of Materials Science, University of Tsukuba Simultaneous observation of millisecond dynamics in atomistic structure, force and conductance on the basis of transmission electron microscopy in solid point contacts Title and affiliation when prize awarded Associate Professor/Lecturer, School of Engineering, Nagoya University

ture, phase transformation, surface modulation and in- Abstract when prize awarded terface formation. This developed in-situ HRTEM also The elucidation of “structures and transformation”, i.e., enabled simultaneous measurements of conductance of how atoms configurate solids and how their arrange- nanostructures and forces acting on them. In particular, ment changes, is a basic subject in condensed matter the experimental basis of the atomic-scale mechanisms physics. Diffraction analyses, such as X-ray methods of materials was established. and various types of static microscopy, have achieved We applied the in-situ HRTEM to study various na- successful outcomes for the former subject “structures,” nometre-sized structures and elucidated the atomistic i.e., the determination of average atomic arrangements structural dynamics during the formation of single atom of solids in stable states. In contrast, these methods have contacts and wires, which are the finest contacts joined not provided sufficient contribution in the latter subject by only one atom and the thinnest wires, i.e., one dimen- “transformation.” Structural dynamics had not been an- sional single atom alignments, respectively. We expli- alysed at the atomic scale although it is focused on as a cated the atomic-scale mechanisms of materials for solid major subject in a tremendous number of studies. This is point contacts (nanometre-sized contacts), resulting in because even if the structures are analysed in a stepwise the discovery of new deformation mechanisms of na- fashion during a process, actual structural dynamics is nostructures in addition to fundamental atomic process never found out. As a result, continuous atomistic struc- of deformation. Other nanostructures, such as fullerene tural dynamics had been studied only via computational molecules, carbon nanotubes and single-molecular junc- science, as exemplified by molecular dynamics calcu- tion structures, were fruitful targets of the developed lations. However, the calculated results could not be in-situ HRTEM. compared with any experimental results. The development of an innovative experimental method, which can Progress in Research chase the motion of individual atoms in solids as a live The awarded study has led to the following progress in broadcast from atomic worlds, had been much awaited research. in condensed matter physics. Scientists and engineers in (1) Single-photon spectroscopy of individual nanostruc this field had also been convinced that the experimental tures under in-situ HRTEM results obtained from the innovative methods lead to the The functions of scanning near-field optical microscopy creation of new devices exhibiting noble functions. Dur- (SNOM) are installed in HRTEM for cathode- and photo- ing an in-situ observation, the observed structures can luminescence spectroscopy of individual nanostructures. be controlled. Take, for example, atomic crafts using an An optical fibre probe, having apertures of several tens of in-situ observation as “an eagle eye” and the operation nanometres in width, is allowed to approach individual as “small hands and tools.” nanostructures, i.e., isolated nanoparticles and nanometre We developed in-situ high-resolution transmission elec- regions in polycrystals, under simultaneous structural tron microscopy (HRTEM) to observe directly atomic observation by in-situ HRTEM. The method directly promotion of solids during mechanical deformation, frac- vides the relationships between atomic arrangements of

28 20 years of the Millennium Science Forum individual nanostructures and luminescence. volume. Also, their surface structures significantly af- (2) Free-space nanometre wiring via nanotip manipulation fect their mechanical, electrical, optical and magnetic Relentless efforts in semiconductor technology have properties. We demonstrated the inherent surface recon- driven nanometre-scale miniaturisation of electronic de- struction of metallic nanowires via the in-situ HRTEM. vices and their interconnections. Free-space writing ena- This study leads to evolution in basic studies relating to bles interconnections of stacked modules, leading to ulti- surface reconstruction and in applications of nanowires mate integration of electronics. We have developed free- used in extremely miniaturised integrated circuits for space nanometre-scale wiring by manipulating a metallic next-generation electronics. nanotip during application. The method is capable of In addition to the above-mentioned studies, my other orig- fabricating wires with widths down to 1 nm and lengths inal research subjects relating to, for example, atomistic exceeding 200 nm, with a breakdown current density of friction, single-atom sharpened needles and high-temper- ~10 TA/m2. Structural evolution and conduction during ature thermal barrier coatings, have roots in the study rec- wire formation can be analysed by direct atomistic ob- ognised by the Sir Martin Wood Prize, in 2000. servation using in-situ HRTEM. (3) Control of the structures and electrical properties of Reflections single molecular or nanoparticle junctions I am especially pleased to express my congratulations As the miniaturisation of integrated circuits advances, on the 20th anniversary of the Sir Martin Wood Prize. I electronics using single molecules and nanoparticles are sincerely appreciate its steering and selection commit- being studied increasingly. Ultimate junctions consisting tees. In particular, I acknowledge Professors Noboru of two electrodes sandwiching a single molecule or na- Miura and Hidetoshi Fukuyama, who were chairs of noparticle are assembled by a nanotip operation during these committees when I was awarded the prize in 2000. in-situ HRTEM. We investigated the atomic configura- It has been almost two decades since I was awarded tion and conductive properties of the junctions. It was the prize. At that time, Jiro Kitaura, former president of found that the conductive properties depend on the inter- Oxford Instruments KK, kindly explained the difficulty face structures of the contacts between the core element and laborious efforts to establish the Millennium Science and electrodes. Thus, the relationship between atomic Forum (MSF). I would like to applaud the great efforts arrangements of the junctions and conductive properties of the committees’ members to promote the MSF for the can be elucidated directly. past 20 years. (4) Transformation from slip to plastic flow deformation I very much appreciate Sir Martin Wood for his warm mechanism of nanometre-miniaturised metals hospitality, especially in his house in Oxford. He showed Various types of nanometre-sized structures have been me and Professor Katsuya Shimizu of Osaka University applied to advanced functional and structural devices. (my fellow prize winner in 2000) a chilling device he Inherent structures, thermal stability and properties are developed when he worked in his laboratory. Tony Ford emphasised when their size is decreased to less than sev- looked after us before the award ceremony and continues eral nanometres, especially, to several atoms. We discov- to do so even today. I thank him very much for his kind ered that such miniaturised structures are deformed via support. a plastic flow mechanism, which has not been observed I would like to express my sincere gratitude to Emeri- in coarse-grained metals. The resultant various irregular tus Professor Ayahiko Ichimiya of Nagoya University. relaxed structures exhibit noble electrical and mechan- He has kindly supported me since I studied at Nagoya ical functions. This study opens a new research field of University, my former affiliation. He introduced many structural control of metallic devices comprised of only famous scientists, including Nobel prize winners, to me, one or several atom(s). which were precious opportunities for a young scientist. (5) Surface reconstruction in nanowires He has advised me on my research direction and guided It is well-known that surface atomic positions are recon- me in my involvement with the MSF. I owe what I am structed due to stabilisation. Such surface reconstruction today to him. has been conducted for general surfaces, which are larger Lecture Trip than the size of reconstructed surface unit cells. Hence, University of Oxford, University of Cambridge the surface reconstructions investigated for large surfaces are not applicable for the surfaces of nanometre-sized Contact Information isolated crystals, such as nanoclusters, nanowires and [email protected] nanotubes, having high ratios of surface area to interior

20 years of the Millennium Science Forum 29 Winner in 2000

Current title and affiliation Professor, Division of Materials Physics, Graduate Katsuya Shimizu School of Engineering Science, Osaka University

1989: B.E. Faculty of Engineering Science, Osaka University 1991: M.E. Graduate school of Engineering Science, Osaka University 1994: Ph.D. Osaka University 1995-1997: Research Fellow of the Japan Society for the Promotion of Science for Young Scientists 1997-2002: Research Assistant, Division of Materials Physics, Graduate School of Engineering Science, Osaka University 2002-2003: Lecturer, Division of Materials Physics, Graduate School of Engineering Science, Osaka University 2003-present: Professor, Center for Science and Technology under Extreme Conditions, Osaka University

Search for superconductivity under ultra-high pressure Title and affiliation when prize awarded Lecturer, Graduate School of Engineering Science, Osaka University

provide both the proof of metallization and super- Abstract when prize awarded conductivity at low temperature. Conductivity meas- We have developed techniques for measuring electri- urements are difficult in general at Mbar-pressures cal resistance and magnetization at ultra-high pres- using DAC because of the wiring problem to the sure and at very low temperature. A diamond-anvil small sample and insulation between the wire and cell (DAC) is popular and the most powerful tool the metal gasket. We succeeded to perform a four- for producing static pressure. We have constructed probe electrical resistance measurement in DAC at a compact non-magnetic DAC specially designed pressure of 250 GPa in non-hydrostatic measure- for low temperature research. We recently attained ments; 10 GPa in hydrostatic ones using a ‘liquid’ to perform electrical measurements above 200 GPa pressure medium where a piston-cylinder type hy- at temperature down to 30 mK by assembling on a drostatic cell delimitates the maximum pressure of powerful 3He/4He dilution refrigerator. The combi- around 3 or 4 GPa. nation of two powerful tools has made it possible to Using these experimental technique, we have studied study the condensed matter physics in unprecedent- searching for metallization and superconductivity in edly wide pressure-temperature range. simple systems such as elements like halogen atoms, One of the most aggressive challenges under high chalcogen atoms, 3d-magnetic metals, and alkaline pressure research is the search for metallic hydrogen metals. Recently, the high-pressure research of super- under its extremely dense phase. The metallic hy- conductivity in heavy-fermion systems is a popular drogen is predicted to show superconductivity even area. We also apply these technical advances to the at room temperature and has long fascinated the area where hydrostatic pressure is required since axi- high-pressure physicists, which exists in fact at the al stress causes the dislocation which is considered to interior of a giant planet such as Jupiter or Saturn. suppress the superconductivity. Another challenge topic is “superconductivity” and “magnetism”. It is well known that a ferromagnetic metal does not show superconductivity and even a Progress in Research small amount of paramagnetic impurities could sup- Generally, "superconductivity" is known as a rare press the superconductivity. However, even in the phenomenon. Superconductivity can be seen in a case of iron, the superconducting transition temper- few compounds, which are made by special treat- ature (Tc) was theoretically predicted to be 0.25 K. ments, however here we suppose that “superconduc- We can expect an appearance of superconductivity tivity” is a rather common phenomenon in general in magnetic metals in its nonmagnetic state under material but caused through variety of the mecha- certain pressure and low temperature. nism. Can all elements be superconductive? “It has Electrical transport measurements in DAC can been already revealed that several elements that are

30 20 years of the Millennium Science Forum not the superconductor at ambient pressure became We aim to produce solid metallic hydrogen and re- superconductive at high pressure. Actually, the num- veal the physical phenomena with technical develop- ber of superconducting elements at ambient pressure ment and an innovative approach. The current pro- is 30, and another 23 elements become supercon- ject also aims for remarkable progress in the study ducting at pressurized condition. Additionally, most of material sciences under high-pressure by further of superconducting materials, include elements, strengthening the application of developments. show a negative pressure effect; the superconducting This will reveal novel physical properties hidden in transition temperature, Tc, decreases by applying ultra-high pressure and construct a new era of sol- pressure. However some elements were found to id-state physics. show the positive effect. Recently I have intensively studied superconductivity in elements not only for understanding the mechanism of superconductivity Reflections but also for searching the unrevealed possibility of Congratulations to the Sir Martin Wood Prize for the material. The new periodic table for supercon- 20 years. It means that 20 years has passed since I ductive elements is shown in Fig. 1 which claims received the award and went on my lecture visit to that elements on the upper-right and upper-left cor- the UK where I got the opportunity to give lectures ner of the table gives higher Tc. At this moment, cal- at Oxford and Cambridge Universities. It was my cium (Ca) reaches almost 30 K, which is the highest second trip to the UK, the first was a two-month low in elements, but it needs pressure exceeding 200 budget visit where I followed my supervisor. I was GPa. surprised that the scale of laboratories was smaller The most attractive among various elements is hy- than expected; only a few postdocs and/or PhD stu- drogen in the condensed phase as solid metallic dents were working with a professor. They do very hydrogen is expected to be a room-temperature su- good research and then move every few years and a perconductor. Also, fluid metallic hydrogen under new research theme comes. Good research themes high pressure and at high temperature may provide will bring good researchers from around the world. important information about the interior of giant Recently fewer Japanese students want to work in planets. However, realization of the solid metallic overseas groups. Is this due to a charming environ- hydrogen requires ultrahigh pressures exceeding 400 ment in Japanese laboratories? I would like to moti- GPa at ambient temperature, which is still challeng- vate them not only to go overseas more, but also to ing for high-pressure experimentalists. enjoy good research.

Lecture Trip University of Oxford, University of Cambridge Fig. 1 Three dimension periodic table for elements. The height of the pillar indicates the highest Tc ever observed in each element. On the upper-right and upper-left corner of the table, the elements Contact Information give the higher Tc. The highest Tc was observed in Ca with 29 K at 217 GPa. [email protected]

20 years of the Millennium Science Forum 31 Winner in 2001

Current title and affiliation Professor, Department of Physics, Keiya Shirahama Keio University

1985: B.S., Department of Physics, Hokkaido University 1987: M.S., Graduate School of Physics, Hokkaido University 1990: D. Sc., Graduate School of Physics, The University of Tokyo 1990: JSPS Research Fellow (ISSP, The University of Tokyo) 1991: Alexander-von-Humboldt Fellow, University of Bayreuth, Germany 1993: Research Associate, ISSP, The University of Tokyo 1999: Associate Professor, Keio University 2009-present: Professor, Keio University Electrons meet helium: Superfluid 3He surface probed by the Wigner crystal Title and affiliation when prize awarded Associate Professor, Department of Physics, Keio University

mobility is dominated by scattering of helium quasi- Abstract when prize awarded particles to the periodically deformed surface. Since Superfluid helium is the purest substance in nature. the quasiparticle spectrum is determined by superflu- The free surface of superfluid helium has been of id energy gap, we can study various gap structures great interest as it is recognized as a surface (bound- of the superfluid A, B, A1 and possible new phases ary) of topological superfluids. My research work and change in gap structures near the surface. The concerning the Sir Martin Wood Prize was the first first order transition between the A and B phases and experimental study of the free surface of liquid he- a nonlinear transport caused by deformation of the lium 3, a fermion isotope of helium, in particular in surface were also clearly observed. the superfluid states.

One can trap many electrons on a free surface of liquid helium. The electrons form a two-dimensional system and undergo a phase transition to the Wigner crystal with a triangular lattice. Since electrons on helium surface was the only system that realizes the Wigner crystal state, the interest of community Fig.1: An illustration of the Wigner solid on a liquid helium surface. Electrons (shown as yellow balls) form a triangular lattice concentrated to understand its properties. With Dr. and press the helium surface. The "dimples" formed beneath Kimitoshi Kono at ISSP The University of Tokyo, each electron produce unique dynamical phenomena. I explored the possibility of utilizing the crystal for the study of helium surface. This idea was successfully proven by a series of experiments. Our early Progress in Research transport measurement of crystal on a liquid helium Liquid helium 3 had been established as a textbook 3 surface showed extremely high electron mobility (μ example of anisotropic fermion superfluid. The 8 2 ~ 10 cm /Vsec), which is still the record of electron situation has been dramatically changing since the mobility in condensed matters. This result not only discovery of topological insulators in 2006. The con- showed the ultra-clean nature of helium surface, but cept of topological insulators was applied to super- also opened the possibility of utilizing surface elec- fluidity and superconductivity, and superfluid helium trons for quantum computing. 3 is realized as a unique topological superfluid. The Wigner solid can be a useful probe for the topologi- We succeeded to measure the mobility of the Wigner cal superfluid, in which intriguing surface phenom- crystal on the surface of superfluid states of helium 3 ena such as Majorana bound states are theoretically down to 200 μK. It was unexpectedly found that the proposed.

32 20 years of the Millennium Science Forum After winning the 2001 Sir Martin Wood Prize I con- UK is the birthplace of the low temperature physics tinued to study the dynamics of the Wigner solid on when Sir Martin showed me the first superconduct- helium 4 and isotopic mixtures, but I have gradually ing magnet made by them. focused my interests to the properties of superfluid I would like to thank the Sir Martin Wood Prize helium itself. I discovered a quantum phase transi- committee, staff of Oxford Instruments, and my tion in helium 4 under nanoscale confinement. This friends and colleagues in the UK who made the discovery has lead me to utilize the confinement ef- lecture trip successful. Last but not least, I would fect for unveiling novel topological properties of su- like to thank Professors Miura and Fukuyama, and perfluid helium 3. My research group at Keio is cur- Mr.Tony Ford, for their continual supports and en- rently conducting experiments on superfluid helium couragement to me since winning the prize. 4 and 3 in well-defined nano/microscale confined geometries and pursuing to search for superfluidity in adsorbed films other than helium.

Reflections Let me write my personal recollection of the Sir Martin Wood Prize ceremony and the following lecture trip. Two weeks before the Ceremony I broke my ankle by slipping on the stairs of Shimokitazawa Station. I almost gave up to attend the ceremony as I was in hospital until a few days beforehand. Eventu- ally I could attend the ceremony with crutches, and somehow gave the prize lecture sitting on a special stage. I was happy that Sir Martin directly awarded me the Prize. I was also pleased that the speaker after me was Dr. Mamoru Mohri, the first Japanese astronaut, because I grew up in the town next to his birthplace in Hokkaido and he has been my hero since the first astronaut selection in Japan. On the lecture trip, I gave talks at Manchester, Roy- al Holloway and Oxford. At that time, Powerpoint presentation was rapidly spreading and I was the first person to use Powerpoint for the prize lecture. In my final lecture in the Martin Wood Lecture Theatre of Oxford, I broke into a cold sweat just a few minutes before the start time as the presentation slide did not appear on the screen of the theatre (it was a common problem then). I felt that my presentation got better as I repeated the same lecture in three universities. I was impressed by some of the famous low temperature physicists who attended my lecture: the UK is the birthplace of low temperature physics, and I Lecture Trip remembered the names of Dewar, Simon, Mendels- University of Manchester, University of Oxford, Royal Holloway, University of London sohn, Kurti and others. The visit to Oxford Instruments and the time spent with Sir Martin and Audrey in their Manor House Contact Information [email protected] were also unforgettable. Again, I realized that the

20 years of the Millennium Science Forum 33 Winner in 2002

Current title and affiliation Professor, Department of Physics, Ichiro Terasaki Nagoya University 1986: B.S., The University of Tokyo 1988: M.S., The University of Tokyo 1988-1990: Doctorate Course, The University of Tokyo 1990-1993: Research Associate, The University of Tokyo 1992: Doctor (Engineering) 1993-1997: Chief Researcher, International Superconductivity Technology Center 1997-2003: Associate Professor, Waseda University 2003-2010: Professor, Waseda University 2004: Visiting Professor, University of Bristol 2010-present: Professor, Nagoya University 2015-present: Cross-Appointment Fellow, National Institute of Advanced Industrial Science and Technology (AIST)

Large thermopower in NaCo2O4 : a novel physical property in transition-metal oxides Title and affiliation when prize awarded Associate Professor, Department of Applied Physics, Waseda University

the common thought at that time was that oxides Abstract when prize awarded were too poor to be used for thermoelectric devices. We discovered a large thermopower and anomalous We tried to uncover the secret of this oxide, and fi- properties in the layered cobalt oxide NaCo2O4 in the nally arrived at the concept that the magnetism and study of reference materials concerning high-tem- electron-electron interaction were crucial. This idea perature superconductors (HTSC). This study has had not been considered in thermoelectric materials accelerated the research field of oxide thermoelec- thus far. trics: the energy conversion technology between heat and electricity using oxide ceramics. Chemists are eager to make many new materials and identify their structures. Once they have done so, The discovery of high-temperature superconductiv- they are often satisfied and leave other properties ity in copper oxides, in 1986, has made two great untouched. The high thermoelectric performance in impacts on basic science. One is to deny the super- NaCo2O4 is a prime example, and I believe that this stition that only a mega-science can discover new indicates the raison d’être of physicists developing physics. The other is to remove the wall between new materials. We physicists can find interesting and physics and chemistry; physicists have begun to syn- useful functions which have been sleeping quietly in thesise many samples, and chemists have begun to old materials that chemists synthesised a long time measure physical properties very precisely. I am one ago. Post-HTSC physicists, including myself, will such physicist, who makes samples, measures prop- search for new functions in existing materials rather erties precisely, and thinks deeply about the meaning than in new materials. of the measured data.

NaCo2O4 is an old material, which was synthesised Progress in Research and identified in the 1970s by French chemists. We As oxide thermoelectrics has been developed wide- succeeded in making single crystals and measured ly, as of July 2018, our discovery paper has received the resistivity and thermopower (voltage proportion- more than 2,700 citations, according to Google al to the applied temperature difference). We found Scholar. In the meantime, applications using thermo- that the measured values were as good as those for electric oxides have been developed, and a venture the state-of-the-art thermoelectric material Bi2Te3 company named TES New Energy, which sells ox- and reported a possibility that NaCo2O4 was appli- ide thermoelectric power generators spun out from cable to thermoelectric devices. AIST. I am a happy scientist because what I found has been accepted by my scientific peers and has This made a great impact to the community because been used in practical devices by engineers.

34 20 years of the Millennium Science Forum Later, TES New Energy developed a cooking pan Martin Wood Prize. equipped with a thermoelectric power generator. It When I was awarded the Sir Martin Wood Prize in was named Hatsuden-Nabe, (which means electrici- 2002, it was the first time I had won a prize in my ty-generating pan). This product became popular and life. Definitely, it launched my career. I would like was distributed in a village in Uganda by a non-gov- to sincerely thank Sir Martin Wood, Professor Nobo- ernmental organisation. In the village, no electric ru Miura, Tony Ford and many others for supporting power is supplied, so residents cannot do anything this prize. but sleep after dinner. The Hatsuden-Nabe with LED Although 16 years have passed since I won, I re- diode gave them light at night, and high school stu- member clearly the lecture trip I took in autumn dents looked happy because they could study at their 2003 as part of the prize. I visited the University of classroom in the evening. When I heard of this news, Bristol for the first time and decided I would take I felt that a small scientific discovery may be able sabbatical leave there in 2004. I’ll also never forget to make our future a bit better. Unfortunately, TES the delightful chats I had with Tony, who kindly New Energy ceased manufacturing, but many photos drove us to the universities we visited. During the and videos are still available on the web (search for drive to Oxford from Cambridge, in the evening, we Hatsuden-Nabe). saw many fireworks quietly lighting up the dark sky I have continued to search for new functions in old in various places. It was Guy Fawkes Night. materials. My next discovery was to observe a giant It was a pity that we did not have the chance to visit non-ohmic resistance in an organic conductor. The the home of Sir Martin Wood, but my wife and I organic sample showed a resistance 1,000-times thoroughly enjoyed the lecture trip, including our smaller simply by changing the current from 1 μA experience of culture in the UK. to 10 mA. This discovery has been developed as a “non-linear conduction in strongly correlated electrons,” and has attracted keen theoretical interest from researchers of string theory and statistical physics. On a cold, wintry day, we see ponds freeze while rivers are flowing. Electrons in solids behave similarly; they are frozen as an ordered state, but the order may be melted by an electron flow, i.e. external current. Finding new materials or, to be precise, finding new functions is a dialogue with a sample. When- ever I talk to the sample through measurement of a Fig.1: Dinner in a restaurant near Oxford during the lecture visit quantity, it always replies through the signal for the measurement. Analysing the reply, I ponder deeply on what property is being kept waiting for measurement. Then I talk to the sample once more through a different measurement, and it replies again. Using this method, the feedback loop is really great fun to me; it shows me that nature is rich, fertile, and pro- found. This is the best moment, I feel, to be a scientist. Lecture Trip University of Bristol, University of Cambridge, University of Oxford, Cardiff University Reflections I would like to express my sincere gratitude and Contact Information [email protected] congratulations on the 20th anniversary of the Sir

20 years of the Millennium Science Forum 35 Winner in 2003

Current title and affiliation Professor, Department of Physics, Toshimasa Fujisawa Tokyo Institute of Technology

1986: B.S. Department of Applied Physics, School of Science, Tokyo Institute of Technology 1991: Ph.D. Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Tech- nology 1991-2008: NTT Basic Research Laboratories 2008-present: Professor, Tokyo Institute of Technology

Single-electron dynamics in semiconductor quantum dots Title and affiliation when prize awarded Senior Research Scientist, NTT Basic Research Laboratories

qubit operations with rotation and phase-shift gate Abstract when prize awarded in a semiconductor double quantum dot. By apply- Electrons play important roles in many systems. ing a voltage pulse, coherent oscillations of a single Nanotechnology allowed us to manipulate single electron between the two dots were successfully electrons one by one and provided unique systems induced. Furthermore, two-qubit operations includ- in which dynamic behaviour of single electrons can ing controlled-NOT gate and swap gate have been be studied. In this work, “Single-electron dynamics successfully demonstrated. in semiconductor quantum dots,” single electron Long spin lifetime: An electron spin in a quantum dynamics were successfully tailored and measured dot is also attractive as a qubit for its long spin re- precisely in a relatively short timescale. laxation time. We have developed an electrical pump- Single-electron ammeter: A quantum dot is a small and-probe scheme to conductive island, in which tuneable numbers of investigate the long spin electrons occupy discrete energy levels. Electrons lifetime. The scheme transport through the dot one by one in the sin- is now widely used to gle-electron tunnelling regime. Each tunnelling measure spin lifetime in event can be monitored various quantum dots. by a sensitive charge The series of works on detector. We have suc- single-electron dynamics in semiconductor quantum cessfully developed a dots has stimulated subsequent developments in na- single-electron ammeter no-electronics and quantum computing. that can measure extremely small current on Progress in Research the order of atto-amperes with a single-electron res- The works on single-electron dynamics in semicon- olution. The single-electron ammeter can be applied ductor quantum dots were extended for studying to various fields that require high sensitivity and charge dynamics in low-dimensional semiconductors. high accuracy in electrical current. In contrast to zero-dimensional states in quantum Semiconductor charge qubit: A double quantum dots, one- and two-dimensional electronic systems dot provides a tuneable have kinetic degrees of freedom, but they are quite quantum two-level sys- different from those in ordinary three-dimensional tem that can be used as systems. The low-dimensional systems are particular- a quantum bit (qubit) ly interesting for studying non-trivial quasiparticles. for quantum computing. We focus on mostly dynamics in the quantum Hall We have successfully effect of a two-dimensional electron system under a demonstrated full one- strong magnetic field. While the central region (bulk)

36 20 years of the Millennium Science Forum is insulating (a kind of topological insulator), one-di- trodynamics (cQED). mensional electrical channels are formed along the We have successfully boundary between the bulk and the outer region (vac- fabricated an elec- uum). Intriguing characteristics of low-dimensional tron-phonon hybrid sys- electrons can be studied in the system. tem, in which a double One-dimensional chiral plasmons: Electron-elec- quantum dot is embed- tron scattering associated with Coulomb repulsion ded in a phonon cavity alters the transport characteristics in one-dimensional for surface acoustic waves (SAW) on a GaAs/Al- conductors. Based on the Tomonaga-Luttinger mod- GaAs heterostructure. The phonon-assisted transport el, spin and charge degrees of freedom propagate in is significantly enhanced at the resonant frequency. different manners in one-dimensional conductors, This is attractive for studying strong or ultra-strong known as spin-charge separation. Previously, such coupling regimes. signatures were detected in the power-law anomaly in the electron transport characteristics. As the theory Reflections suggests, such an anomaly can be understood more When I was an undergraduate student, I was quite easily in terms of plasmons, which are quasiparticle impressed with a charge coupled device (CCD), not excitations originally called spinon and holon. We as an image sensor but as an intriguing transfer ac- have demonstrated clearly how the spin and charge tion of charges in a queue. I was excited by the elec- degrees of freedom are separated in a time-resolved tric control of electrons. This was one of the reasons measurement. Furthermore, the Tomonaga-Luttinger why I started studying semiconductor physics on a model, known as graduate course and, later, single electron dynamics. an exactly solvable Semiconductor nanostructures are fascinating play- model, suggests the grounds, with electrons for engineers as well as presence of many physicists. One can tailor a potential profile in such conserved quanti- a way that electrons travel through a narrow passage ties and the absence (quantum point contact), a few electrons are packed of thermalisation in a container (quantum dot), and electrons move in processes in the system. This is attractive for trans- one direction (quantum Hall edge channel). porting massive information in the one-dimensional I was also excited about more advanced control of channel. We have successfully observed non-thermal electrons with single-electron accuracy. At a low metastable states in our recent experiment. temperature, electron motion is dominated by quan- Electron-phonon hybrid system: Coupling of elec- tum mechanics, where the particle-wave duality trons to phonons has been known to cause scattering shows up. Moreover, interacting electrons exhibit or energy relaxation in semiconductors. This neg- non-trivial motions. In this way, techniques for con- ative effect can be applied in a constructive way to trolling electrons have been developed considerably realise an acoustic analogue of cavity quantum elec- for a few decades. Now, a natural question is what trodynamics (cQED). We have successfully fabri- we can use this advanced technology for. It would be cated an electron-phonon hybrid system, in which a nice to have a meaningful application of intriguing double quantum dot is embedded in a phonon cavity electron features in our life. I hope some young sci- for surface acoustic waves (SAW) on a GaAs/Al- entists will be inspired to extend the work and find a GaAs heterostructure. The phonon-assisted transport real application. is significantly enhanced at the resonant frequency. This is attractive for studying strong or ultra-strong coupling regimes. Lecture Trip University of Cambridge, University of Nottingham, Electron-phonon hybrid system: Coupling of elec- University of Oxford, University of Southampton trons to phonons has been known to cause scattering or energy relaxation in semiconductors. This neg- Contact Information ative effect can be applied in a constructive way to http://fujisawa.phys.titech.ac.jp/ realise an acoustic analogue of cavity quantum elec-

20 years of the Millennium Science Forum 37 Winner in 2004

Current title and affiliation Professor, Faculty of Pure and Applied Yuzo Ohno Sciences, University of Tsukuba

1991: B.S. Department of Electronics Engineering, The University of Tokyo 1993: M.S. Department of Electronics Engineering, The University of Tokyo 1996: D. Eng., Department of Electronics Engineering, The University of Tokyo 1996-2001: Research Assistant, Research Institute of Electrical Communication, Tohoku University 2001-2012: Associate Professor, Research Institute of Electrical Communication, Tohoku University 2012-present: Professor, Faculty of Pure and Applied Sciences, University of Tsukuba

Spin injection and spin control in semiconductors Title and affiliation when prize awarded Associate Professor, Research Institute of Electrical Communication, Tohoku University

a spin Esaki diode and demonstrated electrical elec- Abstract when prize awarded tron spin injection from the valence band of a p-type In order to demonstrate spin injection into semicon- ferromagnetic semiconductor (Ga,Mn)As into the ductors, we fabricated light emitting diodes (LEDs) conduction band of a non-magnetic semiconductor which consist of pn junctions of a p-type ferromag- via interband tunneling. Clear hysteresis loop with netic semiconductor (Ga,Mn)As and non-magnetic ±6.5% remanence is observed in the magnetic field n-GaAs with a strained (In,Ga)As quantum well dependence of EL polarization from an integrated (QW) inserted as an active region. Here, p-type p-(Ga,Mn)As/n-GaAs/(In,Ga)As/p-GaAs LED. (Ga,Mn)As is used as a spin polariser: Spin-polarisation of the injected holes is determined directly from We also investigated electron spin dynamics in the electroluminescence (EL) polarisation emitted GaAs/AlGaAs QWs grown on (110)-oriented sub- after the recombination with unpolarized electrons strates with n-doping, in which the spin relaxation according to the optical selection rule. EL is collect- mechanism predominant for conventional (100) ed from the cleaved facet to minimise magneto-opti- QWs is shown to be substantially suppressed. It was cal effects due to the nearby (Ga,Mn)As, and its po- demonstrated that the spin relaxation time is found larisation was investigated with a variable magnetic to reach nanosecond order in wide temperature field applied parallel to the easy axis of the (Ga,Mn) range by optical time-resolved measurements. This As layer, i.e. in Faraday configuration. We observed has enabled us to investigate nuclear spin dynamics that the EL polarisation below TC draws a clear hys- by optically detected nuclear magnetic resonance. teresis loop: the remanence EL polarisation at zero magnetic field is about 1% at T = 6 K. It follows the magnetization of (Ga,Mn)As, which is inde- Progress in Research pendently measured by a Superconducting Quantum As for the research of spin injection, we investigated Interference Device (SQUID) type of magnetometer. injection of spin polarized electrons in a (Ga,Mn) The presence of hysteretic EL polarisation indicates As∕n+-GaAs Esaki diode (ED) by using a three-ter- that the hole spins can be injected and transported in minal device integrating a (Ga,Mn)As ED and a non-magnetic GaAs. light emitting diode (LED). Electroluminescence po-

larization (PEL) from the LED was measured under Injection of spin polarized electrons, not holes, is the Faraday configuration as a function of bias volt- more preferable from the application point of view ages applied independently to the Esaki diode and to as electrons usually exhibit longer spin lifetime due the LED. The maximum PEL of 32.4% was observed to small spin-orbit coupling. Because of the lack of when the valence electrons near the Fermi energy of n-type ferromagnetic semiconductor, we employed (Ga,Mn)As are ballistically injected into the LED.

38 20 years of the Millennium Science Forum ternal magnetic field with respect to the QW plane. We also directly measured the spatiotemporal evolu- It is likely that the non-uniform EFG as well as the tion of photoinjected local spins of a two dimension- hyperfine interaction governs the inhomogeneous al electron gas in a modulation-doped GaAs/AlGaAs broadening of NMR spectra. quantum well with a top gate electrode by using a time- and spatially resolved Kerr microscopy. The spatial pattern of spins after diffusion is controlled Reflections by a gate voltage that changes the strength of the I would like to express my sincere congratulations spin-orbit interaction (SOI) field. By measuring the on the 20th anniversary of the Sir Martin Wood Prize time dependence of spin distribution with an exter- awarded by the Millennium Science Forum. nal magnetic field, we successfully observe a persis- tent spin helix state by tuning the gate voltage and The Sir Martin Wood Prize is a unique prize in terms obtain both Rashba and Dresselhauss SOI parame- of the grateful opportunity to give a lecture in fa- ters separately. mous UK universities, it was a precious experience for me to improve my presentation skills in English. As for the research on spin coherence in GaAs (110) QWs, we demonstrate manipulation of nuclear During my visit to the University of Oxford, in addition spin coherence in a GaAs/AlGaAs quantum well to meeting faculty staff, I came in touch with the his- by optically detected nuclear magnetic resonance torical culture of the UK, which is a great incentive (NMR). A phase shift of the Larmor precession of for young researchers in Japan. photoexcited electron spins is detected to read out the hyperfine-coupled nuclear spin polarization. I would like to express my sincere thanks to Profes- Multipulse NMR sequences are generated to control sor Noboru Miura and Tony Ford for their kind sup- the population and examine the phase coherence in port during my visit in the UK. quadrupolar-split spin-3/2 75As nuclei. The phase coherence among the multilevel nuclear spin states is addressed by application of pulse sequences that are used in quantum gate operations.

We also demonstrated electrical coherent manipulation of a quadrupolar-split nuclear spin ensemble in a GaAs quantum well (QW) with an rf electric field by the optical time-resolved Kerr rotation technique. Rabi oscillations and phase control between two spin-3/2 states are demonstrated by nuclear electric resonance in a gated GaAs QW device. This enables us to achieve coherent control of geometrically spec- ified nuclear spins.

Furthermore, we obtained strain and electric field gradient (EFG) in an n-GaAs/Al0.3Ga0.7As (110) quantum well (QW) by optically detected nuclear Lecture Trip University of Sheffield, University of Cambridge, magnetic resonance (NMR). The dependence of University of Oxford, University of Southampton the quadrupolar splitting on an angle between the QW plane and a static magnetic field provided the crystalline-orientation-dependent EFG and strain Contact Information in the GaAs QW. We also explored the dependence [email protected] http://www.bk.tsukuba.ac.jp/~oono/ of the NMR line widths on the direction of the ex-

20 years of the Millennium Science Forum 39 Winner in 2005

Current title and affiliation Professor, Graduate School of Frontier Tsuyoshi Kimura Sciences, The University of Tokyo

1991: B.E. Synthetic Chemistry, The University of Tokyo 1993: M.E., Superconductivity, The University of Tokyo 1996: Ph. D, Superconductivity, The University of Tokyo 1996-2000: Postdoc, Joint Research Center for Atom Technology 2000-2003: Lecturer, Dept. of Applied Physics, The University of Tokyo 2003-2005: Limited term staff member, Los Alamos National Laboratory, United States 2005-2007: Member of technical staff, Bell Laboratories, Lucent Technologies, United States 2007-2017: Professor, Graduate School of Engineering Science, Osaka University 2017-present: Professor, Graduate School of Frontier Sciences, The University of Tokyo

Materials design toward gigantic magnetoelectric response Title and affiliation when prize awarded Member of Technical Staff, Lucent Technologies, Bell Laboratories (USA)

accompanied by an unexpected spiral magnetic Abstract when prize awarded order [1]. By using these compounds, we observed Ferromagnets develop a spontaneous magnetisation a gigantic magnetoelectric effect, that is, a con- that is sensitive to an external magnetic field; in a trol of the magnitude and direction of an electric similar fashion, the spontaneous polarisation in fer- polarisation vector by applying a magnetic field. roelectric materials depends on an external electric Furthermore, we proposed that frustrated magnets field. The study of these systems encompasses a con- possessing complex magnetic structures, such as a siderable portion of condensed matter physics. These spiral magnetic structure (Figure), can be promising materials also figure prominently in recent electronic candidates for multiferroics with gigantic magne- devices. However, these two collective properties toelectric effects. Based on these materials’ design (ferromagnetism and ferroelectricity) have been strategy, we found that some other transition-metal investigated mainly as distinct and independent phe- oxides with spiral magnetic orders exhibit remark- nomena. One of the coupling phenomena between able magnetoelectric couplings [2]. Our discovery magnetism and ferroelectricity is the “magnetoelec- has provided a new route to design materials show- tric effect”, that is, the induction of magnetisation ing ferroelectricity with magnetic origin as well as by means of an electric field and that of an electric gigantic magnetoelectric responses. polarisation by means of a magnetic field. This phe- [1] T. Kimura et al. Nature 426, 55 (2003). nomenon attracted some interest in the 1960s and [2] T. Kimura et al. Phys. Rev. Lett. 94, 137201 (2005). 70s, as the effect can provide an additional degree of freedom in device design. However, there have been no applications using the magnetoelectric effect, mainly due to material limitations. Given large magnetic (electric) responses to an external magnetic (electric) field in ferromagnetic (ferroelectric) materials, one approach to achieving a large magnetoelectric response is the use of materials in which Figure : Spiral magnetic structure which breaks inversion sym- ferromagnetic and ferroelectric orders exist simulta- metry and results in ferroelectricity. neously. Such materials are called “multiferroics.” Progress in Research We have explored novel multiferroics showing gi- After our discovery of the giant magnetoelectric gantic magnetoelectric responses. Consequently, effect in TbMnO3, studies on magnetoelectric cou- perovskite-type rare-earth manganese oxides includ- plings and multiferroics have gained renewed inter- ing TbMnO3 were found to exhibit ferroelectricity est in the community of materials science and con-

40 20 years of the Millennium Science Forum densed matter physics. Under such circumstances, ceeded in observing the symmetry breaking due to we have been seeking new magnetoelectric phenom- the helix chiral motif of electric quadrupole mo- ena and materials with higher performances, includ- ments and its domain structure in enantiomorphic ing high-temperature operation and the magnitude of DyFe3(BO3)4 with Dy 4f electric quadrupoles. the effect. In terms of the magnitude of the magnetoelectric Reflections effect, we revealed that TbMnO3 exhibits a pres- Congratulations on the 20th anniversary of the Sir sure-induced magnetoelectric phase transition and Martin Wood Prize! I would like to convey my grat- that the high-pressure phase shows the largest fer- itude to those who have contributed to its activities. roelectric polarisation among magnetically induced I had just joined Lucent Technologies, Bell Labora- ferroelectrics ever reported. Moreover, the ferroe- tories, New Jersey when I received the notice that I lectric polarisation is further enhanced by applying had won the Sir Martin Wood Prize. Looking at the a magnetic field. Its magnitude is comparable to that list of past prize winners, I find that I am the only of conventional ferroelectrics. These results demon- winner who belonged to a foreign research institute strate that it is possible to attain giant spin-driven when the prize was awarded. I was lucky that the ferroelectric polarisation, which comes close to that prize is not restricted to researchers in Japanese in- in conventional displacive ferroelectrics, and to con- stitutes, rather it includes all those whose work is trol it magnetically. performed in Japan. One of our major achievements in terms of A uniqueness of the prize is that a lecture trip to the high-temperature operation is the discovery of a UK is provided to the recipient. Various experiences low-field magnetoelectric effect at room temperature including not only scientific events but also social in some hexaferrites whose crystal structures are ones, to experience British culture during the trip similar to ferrite magnet (refrigerator magnet). We were quite enjoyable and memorable. I remember that demonstrated a magnetic control of ferroelectric po- we stopped in a suburban restaurant and enjoyed fish larisation up to about 400 Kelvin, for the first time, and chips when travelling from Cambridge to Oxford in a Z-type hexaferrite Sr3Co2Fe24O41. Non-volatile in a car driven by Tony Ford. Another uniqueness is electric-field control of magnetism at room temper- the abundant opportunities to interact with other prize ature was also demonstrated in these hexaferrites. winners. From 2011, the MSF has held a Sir Martin More recently, we achieved a magnetic-field control Wood Prize lecture at Osaka every December. I en- of electric polarisation at room temperature in a liq- joyed hosting and listening to one of these lectures uid crystal with a chiral smectic structure. Thus, the when I was in Osaka University. Through this oppor- study of magnetoelectric couplings is not limited to tunity, I was able to chat with not only a new winner inorganic transition-metal oxides. but also former recipients every year. Since the concept of symmetry breakings is crit- In my opinion, the best part of being awarded the ical in magnetoelectric coupling phenomena, we prize is having more opportunities to meet various are expanding our study in this context. We are people, which is by far more valuable than a cash exploiting materials possessing magnetoelectric prize. I appreciate the Millennium Science Forum cluster-multipoles breaking both time-reversal and for giving me such priceless opportunities and be- space-inversion symmetries, which is a require- lieve that I have to do that for young researchers. ment of a linear magnetoelectric effect. Examples Finally, I would like to thank all of my colleagues, of such cluster multipoles are magnetic toroidal and students, and collaborators for their kind support. magnetic quadrupole moments. We designed and synthesized materials involving these multipoles, Lecture Trip and experimentally demonstrated their presence and University of Cambridge, University College Lon- don, University of Oxford, University of Warwick magnetoelectric activities in some transition-metal compounds such as toroidal-glass (Ni,Mn)TiO3 and ferro magnetic quadrupolar Pb(TiO)Cu (PO ) . Contact Information 4 4 4 [email protected] Apart from magnetic multipole moments, we suc-

20 years of the Millennium Science Forum 41 Winner in 2006

Current title and affiliation Prime senior researcher : National Institute of Kazutomo Suenaga Advanced Industrial Science and Technologies

1994: D. Eng., Department of Materials Science, The University of Tokyo 1994-1997: Post-doc, Centre des Materiaux, Ecole Nationale Superier de Mines, France 1997-1998: Post-doc, Solid State Physics Laboratory, University of Paris-Sud, France 1998-2001: Researcher, ICORP Nanotubulites project, Japan Science and Technology Agency (JST) 2011-present: Team leader/Prime senior researcher, National Institute of Advanced Industrial Science and Technology 2015-present: Visiting Professor, Department of Mechanical Engineering, The University of Tokyo

Electron microscopy and spectroscopy on single molecules Title and affiliation when prize awarded Team Leader, National Institute of Advanced Industrial Science and Technologies

molecular imaging, the single atom spectroscopy Abstract when prize awarded and the point defect detection. Imaging and identification of single atoms/mole- [1] K. Suenaga et al., Science 290 (2000) 2280 cules is an ultimate goal of all analytical techniques. [2] J. Dalton, A New System of Chemical Philosophy, by In 2000, we reported the first successful elemen- Russell, (1808) tal identification of individual atoms by means of electron spectroscopy [1]. It came 200 years after the establishment, at the end of the 18th century, of Dalton’s atomic theory, which first proposed distinct elements among atoms [2].

Advances of nanotechnology increasingly rely on the advancement of atomic technologies and therefore the progress of electron microscopies, which are capable of visualising and analysing constituent atoms in individual nanostructures. Electron spectroscopy based on a scanning transmission electron microscope equipped with an energy-loss spectrom- Fig. : The first report of single-atom EELS. (Left) The specimen eter enables us to obtain the chemical composition was Gd@C82 metallofullerenes encapsulated in single-walled of individual quantum objects with high sensitivity carbon nanotubes. (Bottom) EELS spectra recorded on Gd atomic sites shows the signal of Gd M-edge. (Right) The constructed and high resolution, which are crucial to detect do- chemical maps for Gd, for carbon, and a color map (red:Ge, pants or impurities in materials at atomic level. blue:carbon).

Also, a phase contrast of high-resolution transmission electron microscopy with high time resolution Progress in Research and high sensitivity allows dynamic observation Since 2006, I have been more interested in the de- of individual atoms and visualisation of individual velopment of instrumentation because I realised that molecular structures. Point defects such as vacancies the electron microscope must have more potential and pentagons, as well as the Frenkel pair defects to sense individual atoms in nanostructures. With in carbon nanotubes, can be also visualised during a Japanese manufacturer we started two national formation and annihilation. This work highlights projects supported by JST in order to develop high our achievements in atomic-scale characterisation of performance transmission electron microscopes individual nanostructures, involving the individual (TEM/STEM) with geometric and chromatic aberra-

42 20 years of the Millennium Science Forum Fig. : Single atom spectroscopy of dopants in graphene. (a) Cr atom at the graphene edge, (b) Fe atom at di-vacancy, and (c) L2,3core-level EELS clearly indicates that both Cr atom at edge (up) and Fe atom at di-vacancy (bottom) show a high-spin state. tion corrections. Lowering the accelerating voltage and candidates selected for the Sir Martin Wood of TEM/STEM turned out to be essential when one Prize. aims to image any e-beam sensitive object. Obser- I still remember very well my lecture trip to the UK vation of small molecules made of light elements, in 2006. We visited my old friends in Oxford, Leeds, in particular, requires a reduced accelerating volt- Surrey and Cambridge. A most impressive event age, to avoid destroying the molecular structures during the trip was a dinner at St Anne’s College, due to knock-on effects and to enhance the image/ Oxford, which began with grace, delivered in Latin EELS contrast. To compensate for the poorer spatial by Professor Andrew Briggs. It was a great expe- resolution, more sophisticated electron optics are rience for a young Japanese researcher like me to required for the low voltage TEM/STEM, to reduce experience such a British custom for the first time. the residual geometric/chromatic aberrations [1]. Another moving occasion was my visit to Sir Martin Thanks to the projects, the possibilities of sin- Wood at his home. We had a promenade together gle-atom spectroscopy have been extended widely. in the large garden, followed by morning tea with Information on the bonding/electronic states has be- scones and jams made by his wife, Audrey. They come accessible for single atoms through the EELS were so delicious and unforgettable to us. I have not fine-structure analysis as well as the spin state [2]. had a chance to see Sir Martin and Audrey for a long Large variations of local electronic properties of 1D time and hope to have another chance to see them and 2D materials with different atomic coordinates soon. have been revealed. Such an analysis was used to understand catalytic behaviour of Co doped MoS2 for a hydrodeoxygenation reaction as an example of practical applications [3]. Furthermore, a high-energy resolution EELS offers us new possibilities to obtain local optical/vibrational properties. [1] H. Sawada et al., Phys. Rev. Lett., 114 (2015) 166102 [2] Y.C. Lin et al., Phys. Rev. Lett., 115 (2015) 206803 [3] G. Liu et al., Nature Chemistry 9 (2017) 810-816

Lecture Trip Reflections University College London, University of Cambridge, I would like to congratulate the Sir Martin Wood University of Surrey, University of Oxford, Universi- ty of Leeds Prize on its 20th anniversary. I would like to express my appreciation to the secretariat of the forum, without whose devoted support success would not have Contact Information [email protected] been possible, as well as to the steering committee

20 years of the Millennium Science Forum 43 Winner in 2007

Current title and affiliation Professor, Department of Chemical Science and Akira Ohtomo Engineering, Tokyo Institute of Technology

Akira Ohtomo was born in 1972. He studied materials science at Tokyo Institute of Technology and got a doctoral degree of engineering in 2000. After two years postdoc at Bell labs, he moved to To- hoku University in 2002. In 2009, he returned to Tokyo Institute of Technology and initiated his own laboratory. He has published over 180 papers, which are cited over 19,000 times (h-index 59). High-mobility electron gas at polar oxide heterointerfaces Title and affiliation when prize awarded Associate Professor, Institute for Materials Research, Tohoku University

sufficiently high electron mobility to observe the Abstract when prize awarded quantum Hall-effect. In this case, two-dimensional Atomic-scale control of oxide heteroepitaxy is of electron gas (2DEG) was formed in the heterointer- growing importance from the viewpoints of both faces due to strong built-in potential arising from a fundamental physics and device applications. Many spontaneous polarisation mismatch. The density of intriguing physical phenomena such as high-Tc su- 2DEG could be controlled in a wide range by tuning perconductivity, ferromagnetism, ferroelectricity, the Mg content in the MgZnO barriers. and thermoelectricity occur in naturally layered structures of transition metal oxides, giving rise to These results have implications for all oxide het- emergent interests for “epitaxial” design of new erointerfaces, including magnetic tunnel junctions, compounds upon the atomic-scale layer-by-layer Josephson junctions, oxides on semiconductors, etc. growth of artificial superlattices. In particular, the high mobilities achieved present the possibility to combine the world of oxides (su- We developed an ultra-high vacuum-pulsed laser perconductors, multiferroics, colossal magnetore- deposition system equipped with reflection high-en- sistance) with the world of semiconductor hetero- ergy electron diffraction. In this system, rapid opti- structures, including quantum Hall physics. This misation of the growth temperature can be carried work is also a demonstration of the power of the out by using an infrared semiconductor laser heater field of nanoscience to create new physical phenom- that makes a large temperature gradient, enabling ena. This and other recently developed techniques to to realise atomically abrupt heterointerfaces and tailor new materials, atom-by-atom, should continue nearly identical oxygen stoichiometry. Using this to reveal new effects at an ever-accelerating pace. technique, we studied magnetotransport properties of high-mobility electrons at polar oxide heterointerfaces. In the first case, we created a metallic state Progress in Research in an atomically abrupt heterointerface between Recent advances in the epitaxial growth of metal ox- two band insulators, SrTiO3 and LaAlO3, in which ides enable to demonstrate various thin-film devices naturally arising polarity discontinuity introduces for applications of advanced computing and renewa- high-mobility electrons in SrTiO3. As a result, dra- ble energy production. Transition-metal oxides, such matic magnetoresistance oscillations appeared at as TiO2 and α-Fe2O3, are conventional materials uti- low temperatures. Rotation angle dependence of the lised as anodes for photoelectrochemical (PEC) wa- oscillations in the magnetic field suggested three-di- ter splitting because their non-toxic, earth abundant, mensionality of the conducting electrons. Second, and stable nature are advantageous to PEC reactions. we fabricated ZnO/MgZnO heterostructures to attain Our recent research interest is to add new function-

44 20 years of the Millennium Science Forum alities to them by combining the power of epitaxial the prize. He gave me a great opportunity, to be a growth techniques and electrochemical redox reac- supervisor at both Tokyo Institute of Technology and tions. Well-defined thin films with a flat surface and Tohoku University. high crystallinity provide ideal platforms for investigating intrinsic effects arising from the modulation I’m very happy to be a winner of the Sir Martin of compositions, orientation, stoichiometry, and/or Wood prize. I have achieved many things in the 10 electronic states. Moreover, there has been contin- years since I received the prize. First, I was pro- ued focus on controlling competition between Mott/ moted to my current position at Tokyo Institute of Peierls insulators and correlated metals, because Technology. Then I received the JSPS Prize from novel phenomena such as superconductivity and the Japan Society for the Promotion of Science and metal-insulator transition often emerge at the phase the Gottfried Wagener Prize from the German Inno- boundaries. We have made progress on iron for iron vation Award, based on my achievements evaluated oxides and titanium oxides. Starting preparation by prize selection committee. My family and I were of source materials, pulsed laser deposition was pleased that my achievements were honoured with conducted on selected substrates under various con- these prizes. At the same time, the Sir Martin Wood ditions. We also implemented a compact PEC cell prize gave me great confidence as a faculty member and a Li-ion secondary battery structure. Our recent teaching the next generation of researchers. achievements are summarised as follows. (1) band- gap narrowing in solid solutions films of α-Fe2O3 I’m grateful to Professor Noboru Miura and Profes- and Cr2O3, and orientation control of α-Fe2O3 films sor Fukuyama for accompanying me on my lecture resulted in substantial improvement of visible-light trip to the UK, which was truly my real prize. They driven PEC water oxidations. (2) Complete and re- gave me guidance on how I could give a lecture in versible superconductor-insulator transitions in Li- front of a large number of students and researchers,

T2O4 films could be induced by Li-ion electrochemi- in such a way that I did not feel overly tense or panic cal reactions [1]. (3) Superconductivity of Ti4O7 and in response to unexpected questions. Also, from the

γ-Ti3O5 films, with the transition temperatures of 3.0 bottom of my heart I thank Tony Ford, who organ- K and 7.1 K, respectively, was observed despite the ised and facilitated the lecture itinerary, which I was insulating ground states in their bulks [2]. This ap- glad to experience. proach is a powerful way to find new functionalities of materials for sustainable society. Thanks to everyone involved in the prize, including [1] K. Yoshimatsu, M. Niwa, H. Mashiko, T. Oshima, A. those I could not mention, my every working day Ohtomo, Sci. Rep., 2015, 5, 16325. is busy. I’m so sorry that I cannot participate in the [2] K. Yoshimatsu, O. Sakata, A. Ohtomo, Sci. Rep., ceremony to which I’m invited every year, but I 2017, 7, 12544. wish for further progress of the MSF and the professors on the selection committee. Reflections I would like to express my heartfelt gratitude to the Millennium Science Forum (MSF). The Sir Martin Wood Prize, which is marking its 20th anniversary, is widely recognised as a way of promoting young researchers studying condensed matter science. I think that promotion is thanks to the efforts of Lecture Trip Oxford Instruments KK and Professor Hidetoshi University College London, University of Sheffield, University of Oxford, University of Cambridge Fukuyama as well as other professors sitting on the Sir Martin Wood Prize selection committee. I would like to thank Professor Masashi Kawasaki, who Contact Information [email protected] joined the selection committee after I was awarded

20 years of the Millennium Science Forum 45 Winner in 2008

Current title and affiliation Professor, Institute for Chemical Teruo Ono Research, Kyoto University

1991: B.S. Faculty of Science, Kyoto University 1993: M.S. Graduate School of Science, Kyoto University 1996: Ph.D. Graduate School of Science, Kyoto University 1996-1997: Japan Society for the Promotion of Science Postdoctoral Fellow 1997-2000: Assistant Professor, Faculty of Science and Technology, Keio University 2000-2002: Lecturer, Graduate School of Engineering Science, Osaka University 2002-2004: Associate Professor, Graduate School of Engineering Science, Osaka University 2004-present: Professor, Institute for Chemical Research, Kyoto University

Control of magnetisation in nano-magnets by electric current Title and affiliation when prize awarded Professor, Institute for Chemical Research, Kyoto University

as it is based on the quantum mechanical interaction Abstract when prize awarded between the flowing spins and the localised spins It is well known that ferromagnets show the magne- that constitute magnetisation. It is therefore a key to-resistance effect, i.e. the resistivity in ferromagnets technology for future spintronic devices. In fact, depends on the relative angle between the direction IBM proposed a novel storage device called “race- of magnetisation and the electrical current. Thus, track memory,” whose operation relies on the cur- magnetisation controls the flow of the electrical rent-induced DW motion. current. We explored the possibility of the reversed phenomena, i.e. control of magnetisation by electric current. We demonstrated this concept using nano-magnets (magnetic wire or magnetic disk). A magnetic domain wall (DW) exists between two opposite magnetisations (blue and red arrows) in a magnetic wire (Fig.1 (a)). It was found that the injection of electrical current through the wire successfully displaced the DW (Fig.1 (a)-(c)). This current-induced domain DW motion is considered to be a kind of magnetic excitation by a current that flows through a spin structure with spatial variation (DW). This concept Fig. 1: MFM observation of current-induced DW motion. has been tested for another typical noncollinear spin structure: a magnetic vortex. Figure 2 shows a per- spective view of the magnetisation with a moving vortex structure. The height is proportional to the out-of-plane magnetisation component. The rainbow colour indicates the in-plane component as exemplified by the white arrows. On application of the AC current though the magnetic disk, the core starts to make a circular orbital motion around the disk centre, and finally the magnetisation of the core flips into the reversed direction.

The electrical control of magnetisation described is Fig. 2: Current-induced switching of vortex core in magnetic disk. very efficient and scalable down to the nano world,

46 20 years of the Millennium Science Forum the distance between them, by the current injected Progress in Research into the magnetic wire. The DWs were also shifted Rotating magnetic disks (hard disk drives (HDDs)) back and forth depending on the direction of the and semiconductor memories such as static and injected currents. We also demonstrated an all-elec- dynamic random-access memories (SRAMs and trical operation of the magnetic vortex core memory DRAMs) have for many years served as the bed- cell by using a three-terminal device in which the rock technologies for the processor caches, main tunnelling magnetoresistance junction is integrat- memory, and secondary storage in computers. Their ed onto a ferromagnetic disk (Fig. 4). Binary data continued use, however, poses problems with regard corresponding to the core direction can be read out to energy consumption. The most critical problem electrically as the amplitude of the device output and with semiconductor memories is volatility; the in- written electrically by applying a pulsed current. formation they store is lost whenever the computer’s power supply is turned off. They require constant power just to retain the stored information. There is therefore a strong demand for non-volatile memory devices. HDDs are also energy-consuming devices. Although their huge capacity and low cost make them indispensable in our daily life, the mechanical motion required in their operation not only results in the danger of head crashes and other mechanical failures but also wastes energy. Current computers Fig. 4: Demonstration of an all-electrical operation of the magnet- thus use energy even when they are not working and ic vortex core memory cell. can therefore be called normally-ON computers. A normally-OFF computer, or one that uses energy only when doing calculations, is still only a dream. Reflections We made pioneering contributions to the realisation It is my great honour to provide this message as of this dream by demonstrating the basic operation one of the winners of the Sir Martin Wood Prize. I of two kinds of non-volatile magnetic devices: race- would like to thank all the people who led me to the track memory and magnetic vortex core memory. wonderful world of science. Although the possibility Fig. 3 shows the demonstration of the principle op- of technological applications is emphasised here, I eration of racetrack memory. DWs created by the would like to stress that these achievements have local magnetic field induced by a current flowing in originated from fundamental studies on the inter- the writing wire were reproducibly shifted, keeping action between conduction electron spins and local magnetisations. I think all technologies are built on the solid basis of fundamental science that has been created fundamentally by the pure scientific interests of individuals.

Lecture Trip University of Oxford, University of York, Universi- ty College London, University of Cambridge

Contact Information [email protected] Fig. 3: Demonstration of racetrack memory.

20 years of the Millennium Science Forum 47 Winner in 2008

Current title and affiliation Professor, Department of Applied Eiji Saitoh Physics, The University of Tokyo

1996: B.S. in Applied Physics, The University of Tokyo 1998: M.S. in Applied Physics, The University of Tokyo 2001: Ph.D. in Applied Physics, The University of Tokyo 2001-2006: Assistant Professor at Department of Physics, Keio University 2006-2009: Lecturer at Department of Applied Physics, Keio University 2009-2018: Professor at Institute for Materials Research,Tohoku University 2012-2018: Professor, Principal Investigator, WPI-AIMR,Tohoku University 2014-present: Research Director, ERATO (JST) 2018-present: Professor,Dept. of Applied Physics, The University of Tokyo

Discovery of inverse Spin-Hall and Spin-Seebeck effects Title and affiliation when prize awarded Assistant Professor at Department of Physics, Keio University

excitation gap in the insulators is small enough [3]. Abstract when prize awarded [1] E. Saitoh et al. Appl. Phys. Lett. 88 (2006) 182509. We discovered phenomena to detect spin current. [2] K. Uchida et al. Nature 455 (2008) 778-781. Spin current refers to a flow of electron spin angu- [3] Y. Kajiwara et al. Nature 464 (2010) 262-266. lar momentum in condensed matter, which is a spin analogue of electric current. An electron is a particle which carries two quantities: electric charge and (a) internal autorotation called a spin. Spin information is quite fragile in condensed matter; in fact it disap- pears within a very short length scale, such as one thousandth of 1mm in Cu. So, it used to be unimpor- (b) tant. However, this length scale is no longer negligi- ble today; contemporary electronic devices are composed of nanometer-scale structures, much smaller than the spin disappearance length scale. In such a small world, spin current and electric current should be considered on equal footing. However, although physics of electric current in matter is well written (c) in the electromagnetism in matter, no laws were provided for spin current (macroscopic effective theory for spin current was missing); which means that there was no compass to search for spin current phenomena. Our work was the finding of a series of fundamental phenomena of spin current. In particular, the discovery of inverse spin Hall effects [1], the generation of electric fields from spin current, made Fig. 1:(a) Conduction electron spin current (b) Two-particle model of inverse spin Hall effect (ISHE) measurements of spin current possible. By using (c) Electric-field generation from spin current via ISHE. the effect as a spin-current probe, we then explored physical phenomena induced by spin current. One typical outcome is the discovery of the spin Seebeck Progress in Research effect [2] in YIG/Pt: the conversion of heat current After the Sir Martin Wood Prize in 2008, our find- into spin current. Surprisingly, we found spin current ings were recognized as the beginning of the spin can flow even in insulators such as YIG when spin current experimental science. The inverse spin Hall

48 20 years of the Millennium Science Forum effect established itself as a standard spin-current detection method. The effect has been used all over the Reflections world, and so many phenomena were found based I would like to express my sincere gratitude and my on it, such as sound-induced, light-induced, and me- congratulations to the 20th anniversary of the Sir chanical motion-induced spin current generation. Martin Wood Prize. The prize ceremony and the trip The spin Seebeck effect is now used as one of the I had are my cherished and unforgettable memories. most standard methods for spin-current generation, I deeply appreciate the members of the selection and YIG/Pt became a standard spintronics material committee of Sir Martin Wood Prize and the Millen- system most frequently used in spintronics experi- nium Science Forum. ments. Some companies have tried to apply the spin Spintronics is an interdisciplinary field composed Seebeck effect to make thermoelectric convertors of physics, electronics, and material science, pro- to generate electricity from environmental heat. Re- viding a role model for productive collaboration cently, spin current physics is being expanded from among different fields. In electronics, there was a condensed matter science into nano-fluid science, na- great demand for non-volatile memory devices with no-mechanical science, and also into hadron physics. ultralow-energy consumption, which was necessary [4] “Spin current” 2nd edition, Oxford University Press to break-through the wall of energy consumption (2017). problems in computer industries. From the material [5] “Spin current and topological insulators”, Kyoritsu science point of view, there was an established field shuppan (2014). on magnetic materials. The emergence of nanotechnology made it possible (a) to combine these to make devices, but the general principle and concept to create new device functions were still missing. Condensed matter physics played a significant role in such a situation; physics re- searches explored and systematize new phenomena, and gave a guiding principle to find out undiscov- ered phenomena and materials. This was indispensable to establishing the field.

(b) I hope that young researchers in condensed matter science have a broad vision and play an active part vigorously to create new fields. Last but certainly not least, I would like to thank my collaborators on this project, Prof. S. Maekawa, Prof. G.E.W Bauer, their group members, and our students and gradu- ates, especially Dr. K. Ando, Dr. K. Uchida, Dr. Y. (c) Kajiwara, and Dr. Y. Shiomi.

Lecture Trip University of Oxford, University of York, Universi- ty College London, University of Cambridge

Fig. 2:(a) Spin current generation from sound waves and phonons Contact Information (b) Fluid spin -current generation [email protected] (c) Electronics mechanism of fluid spin-current generation

20 years of the Millennium Science Forum 49 Winner in 2009

Current title and affiliation Chief Scientist, Director of Surface and Interface Sci- Yousoo Kim ence Laboratory, RIKEN

1991: B.S., Department of Chemistry, Seoul National University (South Korea) 1993: M.S., Department of Chemistry, Seoul National University (South Korea) 1999: D. Eng. Department of Applied Chemistry, The University of Tokyo 1999-2002: Special Postdoctoral Researcher, Surface Chemistry Laboratory, RIKEN 2002-2006: Research Scientist, Surface Chemistry Laboratory, RIKEN 2006-2009: Senior Research Scientist, Surface Chemistry Laboratory, RIKEN 2010-2015: Associate Chief Scientist, Surface and Interface Science Laboratory, RIKEN 2015-present: Chief Scientist, Surface and Interface Science Laboratory, RIKEN

When a molecule meets electrons Title and affiliation when prize awarded Senior Research Scientist, Surface Chemistry Laboratory, RIKEN

cited molecule, resulting in a much longer lifetime Abstract when prize awarded of excited states, which enable the exploration of The study of single molecules provides deep insights novel reaction dynamics of molecules. Here, I show into the nature of bonding and underlying quantum selective control of reaction pathways of a single mechanics concerning the control of chemical reac- water molecule on an MgO ultrathin film grown on tions. The scanning tunnelling microscope (STM) is a silver single crystal surface (Figure(b)). a versatile and powerful tool for investigating and controlling the chemistry of individual molecules on solid surfaces. The most important feature of the STM is that the tunnelling electrons are involved in its operation. The coupling of tunnelling electrons with the electronic and vibrational states of the target molecule allows us to realise mode-selective and state-selective chemistry of the individual molecules. I will address two main issues with our experimental and theoretical efforts on investigating the interaction of electrons with vibrational and electronic states of a single molecule on surfaces. The first part is assigned to the excitation of vibrational modes to selectively induce particular dynamic motion and chemical reaction of a single molecule on metal surfaces. The microscopic mechanism of vibrationally induced molecular motions and the selection rules for the single-molecule vibrational spectroscopy are also discussed. A precise control of molecular motions and chemical reaction by exciting vibrational modes with an STM will also be explained “Figure (a) A schematic figure of vibrational excitation of a single (Figure(a)). The second part focuses on the novel re- molecule by injecting tunnelling electrons from the STM tip, and action dynamics of a single molecule on an ultrathin the STM images measured before and after single-molecule reaction by vibrational excitation [Phys. Rev. Lett. 89 (2002) 126104]. insulating film surface. The ultrathin insulating film (b) Electron injection from the STM into a target molecule on decouples the molecular orbitals from the metallic the surface of 2-ML MgO film grown on Ag(100), and the disso- ciation pathways of a single water molecule [Nature Materials 9 substrate, to prevent electronic quenching of the ex- (2010) 442].”

50 20 years of the Millennium Science Forum series of lectures in the UK, not only at five universi- Progress in Research ties but also at The Royal Society. Professor Noboru My life work is to describe details of energetic pro- Miura and Tony Ford were with me throughout the cesses, such as energy conversion, transfer and dissi- lecture trip. I cannot express how much I appreciate pation, in a single molecule on solid surfaces by use them for their kind arrangement of the visits and for of single-molecule spectroscopies mainly based on a sharing good times and conversation with me. scanning tunnelling microscope (STM). I am very proud to have been awarded the Sir Mar- My research achievements, which were the main tin Wood Prize even though I am not Japanese; this reason I was awarded the Sir Martin Wood Prize shows the diversity and inclusion in the scientific were the investigation of single-molecule surface community and the Millennium Science Forum. dynamics resulting from the excitation of molecular One of my greatest experiences during the lecture vibration by tunnelling electrons from the STM tip. trip was visiting the house of Sir Martin Wood. He In 2010, the year after I was awarded the Sir Martin showed us a small and old superconducting magnet Wood Prize, I launched my laboratory in RIKEN unit that he made with his wife, Audrey, more than and started the development of a new STM facility 40 years ago. He told us about his great partner- combined with optical excitation/detection systems ship with Audrey during the long history of Oxford to explore electronically excited states and photo- Instruments. From our conversation, I learned the chemical reactions of a single-molecule. Recently, importance of diversity, especially gender and na- with my colleagues, I successfully accomplished tionality, in the scientific, engineering and industrial the construction of the photon-STM systems and communities. I strongly expect a woman to win the reported (1) Development of single-molecule lumi- Sir Martin Wood Prize in the very near future. nescence/absorption spectroscopy [Phys. Rev. Lett. 119 (2017) 013901], (2) Visualization of energy transfer between two molecules [Nature 538 (2016) 364], (3) Photochemical reaction by excitation with visible light [J. Am. Chem. Soc. 139 (2017) 3115], and (4) First demonstration of single-molecule chemical reaction by use of localised surface plasmon [Science 360 (2018) 521]. Development of the novel nanospectroscopic methodologies opens a new way of closely looking at how energy is converted, transferred and demised at various kinds of molecular interfaces and surfaces by visualising geometric/ electronic structures at atomic/molecular level. We are making further challenges to cover a wider range of energy and time domains simultaneously.

Reflections I would like to congratulate the Millennium Science Forum (MSF) on the 20th anniversary of the Sir Martin Wood Prize. One cannot admire enough the Lecture Trip great contribution by the MSF and Sir Martin Wood University of Liverpool, University of Nottingham, Prize to the facilitation and promotion of condensed University of Warwick, University of Oxford, Uni- versity College London, The Royal Society matter physics in Japan, especially by encouraging young scientists and bilateral cooperation within scientific communities in Japan and the UK. Contact Information http://www.riken.go.jp/Kimlab/index.html As a prize winner, it was my great honour to give a

20 years of the Millennium Science Forum 51 Winner in 2010

Current title and affiliation Professor, Depart- ment of Physics, Tokyo Institute of Technology, Shuichi Murakami Professor, TIES, Tokyo Institute of Technology

1993: B.S. Department of Physics, The University of Tokyo 1995: M.S. Department of Physics, The University of Tokyo 1996-2007: Research Associate, The University of Tokyo 1999: Ph.D. Department of Physics, The University of Tokyo 1999-2000: Visiting Research Associate, Stanford University (USA) 2007-2012: Associate Professor, Tokyo Institute of Technology 2007-2011: Research Scientist, PRESTO, Japan Science and Technology Agency 2012-: Professor, Department of Physics, Tokyo Institute of Technology 2012-: Professor, TIES, Tokyo Institute of Technology Theory of the spin Hall effect Title and affiliation when prize awarded Associate Professor, Department of Physics, Tokyo Institute of Technology

Another topic of recent interest, which arose from Abstract when prize awarded the SHE, is quantum spin Hall (QSH) systems (top- The new field of electronics using the spin degree ological insulators). In QSH systems, the bulk is of freedom is called spintronics. The fundamental gapped and insulating, while the edge or surface question in spintronics is how to operate spins and states are gapless and carry spin current. We pro- induce spin current in solids. Because the spin car- posed that bismuth ultrathin film is a good candidate ries magnetism, a naïve way to produce a spin cur- for the QSH system. This prediction has opened the rent is to use a ferromagnet. way for the experimental discovery of Bi1-xSbx as a In my research, I propose another way of producing three-dimensional topological insulator. a spin current in solids, but without a magnetic field. I address our theoretical proposal for intrinsic spin Hall effect (SHE), where an external electric field induces a transverse spin current in semiconductors and metals as shown in Fig. 1. This is caused by the “Berry phase in momentum space,” based on the wave nature of electrons. Since our theoretical proposal, this effect has been observed in various semiconductors and metals. The most prominent among Fig.1 Schematic figure of the spin Hall effect. them is platinum, where the SHE survives even at room temperature. This prominent SHE in platinum can be understood from its band structure. This effect enables us to inject or detect spin current in metals and semiconductors with a simple setup and has already been used as an experimental tool for characterising spin-transport properties of various materials. Because the wave nature of electrons is necessary Fig.2 Imbert shift: an example for the spin Hall effect of light for the SHE, one can expect a similar effect for other types of waves such as light (electromagnetic wave). We find that the SHE of light appears where Progress in Research the refractive index varies spatially. In the case of The central fields of my research are condensed mat- interface between different media, this SHE appears ter theories on topological phases and spintronics. as the Imbert shift, i.e. the transverse shift at the in- In the field of topological phases, we have been try- terface (Fig. 2). ing to invent new concepts and combine them with

52 20 years of the Millennium Science Forum real materials. Our proposal, in 2006, that the bismuth ultrathin film is a two-dimensional topological Reflections insulator, is one of the earliest proposals of topo- I congratulate the Millennium Science Forum (MSF) logical materials. It was experimentally verified in on the 20th anniversary of its Sir Martin Wood Prize 2013. Furthermore, I invented the concept of Weyl and express my sincere gratitude to its committee semimetals, through the study of phase transitions members and staff for their continuous efforts. It is between a topological insulator and a normal insula- my great pleasure to see outstanding, young award tor. I showed, in 2007, that the Weyl nodes in three winners every year. dimensions must be stable and therefore should I have been trying to theoretically propose new phe- also exist in real materials. This proposal had not nomena that can be observed in real materials. Luck- been paid much attention, until the paper by Wan et ily, various phenomena that I proposed have been al., in 2011, on the existence of Fermi arc surface verified experimentally, which is a great pleasure to states. Now the Weyl semimetals are a hot topic, me. My research field is mainly model calculations both in theories and experiments on topological in condensed matter theory. Model calculations materials. Furthermore, we have been collaborating may sound easy; indeed, that thought is partially with researchers in the first-principle calculations true because once a model is constructed, it is often to propose new topological materials. For exam- straightforward to calculate its physical properties. ple, we showed that Te (tellurium) becomes a Weyl The most difficult part is to build simple models that semimetal at higher pressure, and that Ca (calcium) capture novel properties of condensed materials. It becomes a nodal-line semimetal at higher pressure. is not at all a simple task, because the models should In the field of spintronics, we have been trying to be simple for calculations but, at the same time, suf- propose new phenomena from theoretical view- ficiently general to cover a broad range of materials. points. After our theoretical proposal of the spin Hall I believe that good theories should be simple and effect, we theoretically proposed topological mag- beautiful. I think I have managed to build some sim- nonic crystal, where magnons have a gap in the bulk ple theories in condensed matter physics in some but support topological chiral edge modes in the gap, of my work, such as the proposal of the spin Hall similar to those in the quantum Hall system. In this effect, the prediction on the bilayer bismuth thin film proposal we focus on the dipolar interaction between as a two-dimensional topological insulator, and the magnetic moments, because the typical length scale proposal of the Weyl semimetal in condensed ma- for the dipolar interaction is micrometres, which is terials. In the future, I will continue to work in this within state-of-the-art fabrication techniques. We direction, to explore new directions in condensed proposed several structures of topological magnonic matter physics. crystals by combining two different ferromagnets, I would like to thank my collaborators and supervisors, or by putting ferromagnetic dots, both in a spatially especially Professor Naoto Nagaosa and Professor periodic way. We also reformulated the theory of Shoucheng Zhang for their advice, encouragement magnon thermal Hall effect and derived a new for- and scientific discussion. I am also grateful to the mula for the thermal Hall conductivity of magnons. students and staff in my lab for their continuous col- Our formula serves as a standard formula for cal- laboration and support. Last, but not least, I would culating this effect. We also theoretically proposed like to thank my wife, children, and parents for their new variants of the Edelstein effect. The Edelstein continuous encouragement and support. effect refers to the phenomenon where the current in the system induces spin polarisation due to the spin- Lecture Trip split bands of the crystal. In contrast, we found that Lancaster University, University of Nottingham, a current induces an orbital magnetisation when the University of Oxford, University of Manchester, University College London crystal has a chiral structure. We also showed that this effect is anomalously enhanced from its classical analogue, a solenoid. We call this effect an orbital Contact Information [email protected] Edelstein effect.

20 years of the Millennium Science Forum 53 Winner in 2011

Current title and affiliation Associate Professor, Labo- ratory for Future Interdisciplinary Research of Science Yukio Kawano and Technology, Tokyo Institute of Technology

1996: B.S. Department of Basic Science, The University of Tokyo 1998: M.S. Department of Basic Science, The University of Tokyo 2001: Ph.D. Department of Basic Science, The University of Tokyo 2001-2006: Assistant Professor, Department of Physics, The University of Tokyo 2006-2011: Research Scientist, RIKEN 2011-2016: Associate Professor, Quantum Nano-electronics Research Center, Tokyo Institute of Technology 2016-present: Associate Professor, Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology Terahertz wave detection based on low-dimensional electron systems Title and affiliation when prize awarded Associate Professor, Quantum Nano-electronics Research Center, Tokyo Institute of Technology

ductor chip. The development of this device allowed Abstract when prize awarded us to achieve sub-wavelength resolution for the Sensing and imaging with terahertz (THz) waves is wavelength of 100-300 µm. Electronic and molecu- an active area in modern optical science and technol- lar structures of quantum semiconductors, plasmonic ogy. The advantageous properties of terahertz (THz) devices, and polymers were visualized with this im- waves, such as the important energy spectrum in the aging device. meV range, enable various applications of imaging 3) Wide-band, frequency-selective THz spectrome- and spectroscopy. However, since the THz region is ter with graphene located between electronic and photonic bands, even We succeeded in observing THz photoconductivity basic components like detector and source have not of Dirac fermions in graphene, ranging over a wide been fully established, compared to other frequency frequency band of 0.8-33 THz. This result demon- regions. The THz wave also has the problem of low strated that the graphene device works as a wide- imaging resolution, which results from a much longer band, frequency-selective THz spectrometer. We wavelength than that of the visible light. By employ- also imaged potential fluctuations in the graphene ing nanoelectronic materials and devices based on device, suggesting the strong relation to the THz a carbon nanotube (CNT), graphene, and a two-di- photoconductivity. mensional electron gas (2DEG) in a semiconductor Our technologies and findings provided new insights heterostructure, we developed novel types of THz into low-energy and low-frequency dynamics in sensing and imaging devices: physics and chemistry. 1) THz-photon sensor with a CNT/2DEG hybrid device Progress in Research In order to achieve highly sensitive THz detection, I am proceeding with THz science and technology we studied THz response of a CNT/2DEG hybrid research. Our recent major achievements are the de- device. The utilization of this device structure ena- velopments of carbon-based THz flexible cameras bled the detection of THz photons. [1-3] and plasmon-based near-field spectroscopic 2) Near-field THz imager with sub-wavelength reso- imagers [4,5]. lution Most real objects have various three-dimensional The development of near-field THz imaging had curvatures; however, conventional THz imaging sys- been hindered by the lack of high transmission wave tems are mainly restricted to flat samples, hampering line and the low sensitivity of commonly used detec- accurate measurements of such curved objects. We tors. We produced a newly designed THz near-field have recently developed a wideband, flexible and imager, in which all the components: an aperture, a wearable THz camera based on an array of CNT probe, and a detector are integrated on one semicon- THz detectors, which has enabled multi-view THz

54 20 years of the Millennium Science Forum inspections without using bulky systems. This new id-state physics and devices including semiconduc- imaging technology has been achieved based on (1) tors, CNTs, and graphene. As a result I have been thermal device design for enhancement in camera engaging in nanoscale THz science and technology performance such as sensitivity, detection speed, inspired by condensed-matter physics. I strongly and spatial resolution, (2) microscale free-standing feel that science and engineering are closely linked. CNT film arrays, and (3) a gate-free tunable doping I have enjoyed challenging an unknown field and technology based on a variable-concentration dopant pursuing the possibility of new fundamentals and solution. applications. Therefore I believe that collaboration Plasmonic structures are useful for evanescent-field across academic fields to deepen one's own research detection and analysis thanks to their outstanding fields and discover new areas contributes to the fu- properties of high field enhancement and concen- ture development of science. tration in a subwavelength region. In spite of large I have work experience in both universities and availabilities, a main shortcoming of existing plas- research institutes. Looking back on my career, for- monic devices is that they never show resonant fre- tunately I was always in a free environment where quency tunability for fixed structures, which limits there were no walls between research fields. I was the usable range of THz-plasmon-based applications. encouraged to discuss with scientists in different We have developed multi-frequency-resonance fields. This experience taught me how important plasmonic structures and have applied them to sol- open mindedness to different cultures and values is id-state physics research and medical examination, to open up a new field. I am currently collaborating including visualization of electron injection into a with a medical doctor, even though I was afraid quantum Hall conductor and spectroscopic analysis to go to a hospital in my childhood! I believe that of mouse organs. Our techniques can be used effec- anybody can change unless they put limits on their tively for THz sensing and imaging over a broad potential. range of length scales from nanometre to metre. The various prize events provided me with tremen- dously stimulating experiences. In particular, the [1]D. Suzuki, S. Oda, and Y. Kawano, Nature Photonics lecture trip to the UK had a significant impact on 10, 809-814 (2016). me. I was so impressed by the story behind the in- [2]D. Suzuki, Y. Ochiai, and Y. Kawano, ACS Omega 3, vention of superconducting magnets by Sir Martin 3540–3547 (2018). Wood. I was told that he strived to wind supercon- [3]D. Suzuki, Y. Ochiai, Y. Nakagawa, Y. Kuwahara, T. ducting wires at a time when there were no magnetic Saito, and Y. Kawano, ACS Applied Nano Materials 1, resonance imaging instruments. This story always 2469–2475 (2018). reminds me of one of the most important attitudes [4]Y. Kawano, IEEE Transactions on Terahertz Science as a researcher: simply and honestly follow our own and Technology 6, 356-364 (2016). (Invited paper) interests and passions. This should lead us to suc- [5]T. Iguchi, T. Sugaya, and Y. Kawano, Applied Physics cessful results. Letters 110, 151105-1-4 (2017). I am sure that this unique and prestigious prize will further stimulate young researchers in con- Reflections densed-matter science. I would like to express my I would like to express my sincere gratitude on the congratulations once again to Sir Martin Wood, 20th anniversary of the Sir Martin Wood Prize. It was the Millennium Science Forum, and the committee my great honor to receive one of the highest-level members, and wish further success in their activities. prizes in condensed-matter science. Encouraged by receiving this prestigious prize, I have been pushing Lecture Trip forward my successive research activities. University of Cambridge, University of Manchester, University of Oxford, University College London I started my research career from the study on semiconductor physics, especially the quantum Hall effect. My interest gradually shifted to terahertz Contact Information [email protected] waves, but my focus was also on the basics of sol-

20 years of the Millennium Science Forum 55 Winner in 2012

Current title and affiliation Associate Professor, Department of Applied Daichi Chiba Physics, The University of Tokyo 2000: B.S. Department of Electronic Engineering, Tohoku University 2001: M.S. Department of Electronic Engineering, Tohoku University 2004: Ph.D. Department of Electronic Engineering, Tohoku University 2004-2008: Researcher, Japan Science and Technology Agency’s Exploratory Research for Advanced Technology 2008-2012: Assistant Professor, Institute for Chemical Research, Kyoto University 2010-2014: Researcher, Japan Science and Technology Agency’s Precursory Research for Embryonic Science and Technology 2012: Associate Professor, Institute for Chemical Research, Kyoto University 2013-present: Associate Professor, Department of Applied Physics, The University of Tokyo Electric field-induced ferromagnetic phase transition in semiconductors and metals Title and affiliation when prize awarded Associate Professor, Institute for Chemical Research, Kyoto University

effect structures with a channel made of III-V ferro- Abstract when prize awarded magnetic semiconductors or 3d ferromagnetic tran- Electrical control of magnetism adds a new dimen- sition metals. sion to future spin-based information processing I would like to thank H. Ohno, T. Ono, T. Dietl, F. methods. Use of an electric field instead of an elec- Matsukura, K. Kobayashi, S. Ono, and members of tric current is expected to make ultra-low power Ohno and Ono labs for their help. driving devices possible. Ferromagnetic semiconductors had been the central material for this kind [1] H. Ohno and D. Chiba et al., Nature 408, 944 (2000). of research because their magnetic properties are a [2] D. Chiba, M. Yamanouchi, F. Matsukura, and H. function of the carrier concentration. Ohno, Science 301, 943 (2003). We have reported, for the first time, on the electric [3] D Chiba et al., Nature 455, 515 (2008). field control of the ferromagnetic phase transition [4] M. Weisheit at al., Science 315, 349 (2007). and tuning of the Curie temperature using (In,Mn) [5] T. Maruyama et al., Nature Nanotechnol. 4, 158 As in 2000, a ferromagnetic semiconductor [1]. We (2009). also reported, in 2003, an electric field-induced co- [6] M. Endo et al., Appl. Phys. Lett. 96, 212503 (2010). ercivity change, and an electric-field assisted mag- [7] D. Chiba et al., Nature Mater. 10, 853 (2011). netisation switching was demonstrated by using it [8] K. Shimamura and D. Chiba et al., Appl. Phys. Lett. [2]. We also demonstrated, in 2008, that the magne- 100, 122402 (2012). tisation direction can be manipulated by electrically [9] D. Chiba et al., Nature Comm. 3, 888 (2012). controlling the magnetic anisotropy of (Ga,Mn)As [3]. These efforts open up an entirely new route for electrical magnetisation switching without using Progress in Research a magnetic field or current. Although one of the We have focused continuously on the control of problems had been a low Curie temperature of the magnetism in materials. We have found that the ferromagnetic semiconductors, after our findings the magnetic moment induced in a non-magnetic mate- electric field-induced change in magnetic properties rial (Pd or Pt) can be modulated by an electric field using ferromagnetic ultra-thin metals even at room application [10,11]. The results have led to deeper temperature has been reported [4-9]. Using ferro- understanding of the physics behind the effect. From magnetic ultra-thin metallic cobalt, we realised the the application viewpoint, we have shown that even electric field-induced ferromagnetic phase transition the Faraday effect can be switched based on electric around room temperature [7,8]. field-induced ferromagnetic transition in Co [12]. I will show the experimental results of electric field Using this technique, we demonstrated that the control of various ferromagnetic properties in field transmitted light can be switched on and off. This

56 20 years of the Millennium Science Forum may be useful as a miniaturised optical switch in discoveries from the result is critical for making the an optical integrated circuit. We have also proposed next connection in research. These experiences have that the electric field-induced phase transition can shown me that assumptions or a narrow prospective realise a domain wiring in a magnetic race track [13]. pose a potential risk to losing sight of finding seeds In this demonstration, we used a magnetic track with that may lead to breakthrough progress in future re- a ferromagnetic gate electrode. In this device, the search; I learned that meaning can be understood by magnetisation of the gated area returns to the same experiencing something first-hand. My present mot- direction as that of the ferromagnetic gate electrode to is to enhance my professional research ability by owing to its stray field when the ferromagnetism of delving into one subject (enjoying research activity) the gated area is restored by turning off an electric while having a spirit to challenge what is regarded field. Thus, writing operation can be realised simply as impossible using common sense (simply trying). I by switching an electric field on and off without any would like to continue to enjoy research activities by Oersted field application or current injection. In this experiencing various things and by absorbing posi- structure, the domain writing is only one way, but tively what I learn. the reversed domain can be shifted by the electrical Without great support from many people I could current injection into the magnetic track. Therefore, have not received the Sir Martin Wood Prize. Par- the information can be written repeatedly. ticularly, I wish to express my deep appreciation for We have also worked on integrating spintronics and the guidance and support of Professor Hideo Ohno flexible electronics. We have been able to detect not of Tohoku University and Professor Teruo Ono of a magnitude but a direction of strain using a giant Kyoto University. I have come to understand various magnetoresistive (GMR) device fabricated on a flex- perspectives and attitudes concerning research from ible substrate [14]. The GMR device with strain-sen- them. I think they value the enjoyment of research sitive and insensitive ferromagnetic layers separated and free ideas. What I have learned in their labs is by a non-magnetic layer was used to realise this. I really helpful for the present research and supervi- believe that the integration of spintronics and flex- sion of my lab in The University of Tokyo. ible electronics will establish a novel interdiscipli- I also would like to thank the selection committee of nary research field based on science and engineer- the Sir Martin Wood Prize; the steering committee of ing. the Millennium Science Forum; the British Embas- sy, Tokyo; the Embassy of Japan in UK and Oxford [10] A. Obinata and D. Chiba et al., Scientific Rep. 5, Instruments KK. I think the lecture trip, including 14303 (2015). the Sir Martin Wood Prize, is truly unique among [11] K. Yamada, D. Chiba, and T. Ono et al., Phys. Rev. academic awards. I really enjoyed the trip and it was Lett. 120, 152703 (2018). a precious opportunity for me. [12] Y. Hibino and D. Chiba et al., Appl. Phys. Express 10, 123201 (2017). [13] Y. Tanaka, T. Hirai, T. Koyama, and D. Chiba at al., Appl. Phys. Express 11, 053005 (2018). [14] S. Ohta, A. Ando, and D. Chiba, Nature Elec. 1, 124 (2018).

Reflections Lecture Trip I have been inspired by many researchers and could University of York, University of Nottingham, Uni- find hints for my future research subjects from con- versity of Cambridge, University of Oxford, Uni- versity College London versations and discussions with them. These hints and interactions have often become the motivation of my research activities. In addition, I have learned Contact Information [email protected] that simply trying first and picking up unexpected

20 years of the Millennium Science Forum 57 Winner in 2013

Current title and affiliation Professor, Institute of Engineering Innovation, Naoya Shibata School of Engineering, The University of Tokyo

1997: B.S. Department of Materials Science, The University of Tokyo 1999: M.S. Department of Materials Science, The University of Tokyo 2003: D. Eng., Department of Materials Science, The University of Tokyo 2003-2004: Overseas Research Fellow of the Japan Society for the Promotion of Science 2004-2007: Research Associate, Institute of Engineering Innovation, The University of Tokyo 2007-2011: Assistant Professor, Institute of Engineering Innovation, The University of Tokyo 2011-2017: Associate Professor, Institute of Engineering Innovation, The University of Tokyo 2017-present: Professor, Institute of Engineering Innovation, The University of Tokyo Development of an advanced scanning transmission electron microscope for material science research Title and affiliation when prize awarded Associate Professor, Institute of Engineering Innovation ,The University of Tokyo ed-type STEM detector capable of atomic-resolution Abstract when prize awarded imaging and proposed new imaging possibilities by Understanding the atomic-scale structures of surfac- controlling detector geometries: annular bright-field es and interfaces is essential to control the functional (ABF) imaging and atomic-resolution differential properties of many materials and devices. Recent phase contrast (DPC) imaging. ABF-STEM imaging advances in aberration-corrected scanning transmis- enables us to directly visualise light element atomic sion electron microscopy (STEM) have made pos- columns of materials. DPC-STEM imaging can be sible the direct characterisation of localised atomic used to detect local electric fields inside materials structures in materials, especially at interfaces. and devices. We applied DPC imaging to atomic res- In STEM, a finely focused electron probe is scanned olution STEM and succeeded in directly observing across the specimen and the transmitted and/or scat- electric field distribution inside atoms for the first tered electrons from a localised volume of the mate- time. This new imaging capability should assist our rial are detected by the post-specimen detector(s) as a fundamental understanding of the origins of proper- function of raster position. By controlling the detec- ties in materials and devices. tor geometry, we gain flexibility in determining the contrast characteristics of the STEM images and the formation mechanisms involved. Thus, it may be pos- Progress in Research sible to obtain further useful information by exploring The resolution of electron microscopes continues to new detector geometries in atomic-resolution STEM. be improved year by year because of rapid progress From 2006, we have been developing a segment- in the development of aberration correction lens

Fig.1:Experimental atomic electric field imaging of a BaTiO3 single crystal using atomic-resolution differential phase contrast STEM.

58 20 years of the Millennium Science Forum systems. In 2017, our group in The University of Tokyo and JEOL Ltd. (a world leader in electron microscopes) attained world record spatial resolution of 40.5 pm through state-of-the-art aberration-corrected STEM. 40.5 pm is even smaller than the Bohr radius, which means that we can make an electron probe smaller than the size of a single atom. Using such a small probe, it is now possible routinely to directly visualise atoms inside materials and devices. Fig.2:Normal atomic-resolution STEM image (left) and two-di- However, my current interest is whether we can go mensional electric field vector map (right) of SrTiO3 crystal observed along [001] direction [Nature Comm. (2017)]. beyond simply seeing atoms. When I received the 15th Sir Martin Wood Prize, in 2013, I started trying to observe the electric field at Reflections atomic dimensions using DPC STEM with a high- First, I would like to congratulate the Sir Martin speed segmented detector. After several years, we Wood Prize on its 20th anniversary. It was my great- came to the stage that we could map out more pre- est honour and pleasure to be awarded the 15th Sir cisely and quantitatively the electric field distribution Martin Wood Prize. Indeed, my research direction inside atomic columns in crystals and even inside and career has been largely influenced by this prize, single atoms. The Figure shows a normal atom- in a very good way. ic-resolution STEM image and a two-dimensional My lecture tour to the UK, in particular, was a great electric field vector map of SrTiO3 crystal observed opportunity for me to think deeply about my past, simultaneously. The colour contrast corresponds to current and future research directions. I remember the relative direction and strength of the electric field vividly the wonderful time I had while visiting five at each raster position in the image. Compared with famous universities in the UK. I met many scientists the simultaneous normal atom image, disks of rotat- and students and had very stimulating and exciting ing colour contrast are seen at each atomic column discussions. Of course, I also enjoyed the beautiful position in the electric field image. The direction scenery, history, culture, food (and beer!) of the UK. of rotating colour contrast points outward from the It was an unforgettable experience to visit Sir Martin centre of the atomic columns. This is because we are Wood and his wife Audrey at their home. Sir Martin observing the electric field between the positively kindly showed me The Manor House, which was charged atomic nucleus and the negatively charged very impressive, as well as some places that played electron cloud that surrounds it. Thus, by combin- a role in the history of Oxford Instruments. I think ing the highest resolution STEM and the developed this lecture tour makes the Sir Martin Wood Prize DPC imaging technique, we are now directly ob- very different from others; it is outstanding. I really serving inside the structure of atoms in real-space! hope the Millennium Science Forum and Oxford In- This atomic electric field should possess information struments will continue this very important activity about the atomic species, local chemical bonding to encourage and stimulate many young scientists and charge redistributions in between bonded atoms, in Japan, the UK and even worldwide. I also hope so our next challenge will be to directly visualise many ambitious, talented young researchers will be electron distribution in between atoms, i.e. bonding. continuously turned out through this great prize. Also, we are developing a novel atomic-resolution electron microscope that realises a magnetic field Lecture Trip free environment at a sample position. This new mi- University of Glasgow, University of Manchester, croscope will be useful for studying atomic scale University of York, University of Oxford, University of Cambridge, Daresbury Laboratory phenomena of magnetic materials and devices. Direct magnetic structure imaging at atomic resolution will be my next big challenge, too. Contact Information [email protected]

20 years of the Millennium Science Forum 59 Winner in 2014

Current title and affiliation Associate Professor, Department of Physics, The Masamitsu Hayashi University of Tokyo & Group leader, Spin Physics Group, National Institute for Materials Science

2000: B.S., Applied Physics, Tohoku University 2002: M.S., Applied Physics, Tohoku University 2007: Ph.D, Stanford University, Materials Science and Engineering 2007-2008: Post-doctoral fellow, IBM Almaden 2008-present: Senior research scientist, National Institute for Materials Science 2016-present: Associate Professor, Department of Physics, The University of Tokyo Effective field measurements and spin torque dynamics in magnetic nanostructures Title and affiliation when prize awarded Senior research scientist, National Institute for Materials Science

Key to the generation of spin current is the strong Abstract when prize awarded spin orbit interaction of the material. Using a hetero- The control of electrons spin orientation in solids is structure that consists of a paramagnetic metal layer the holy grail of Spintronics research. A particular fo- with strong spin orbit interaction and a few atomic cus has been placed on manipulating the electrons’ layer thick ferromagnetic layer, we have studied the spin orientation by electrical means, that is, to con- current induced effects on the magnetization. Spin trol the magnetization direction of ferromagnets by current generated from the paramagnetic layer via passing current or applying electric field to the sys- the "spin Hall effect" exerts torque on the magnet- tem. The "spin transfer torque" allows such electri- ization of the ferromagnetic layer, causing mag- cal control of magnetization: a spin polarized current netization switching and motion of domain walls. generated by passing current into a ferromagnetic Using unique transport measurements, we revealed layer can be supplied to another ferromagnetic layer the unique characteristics of the torque that occur at to switch its magnetization direction. the paramagnetic/ferromagnetic layer interface. In We have studied the current induced motion of addition, we find that the chirality of the magnetic magnetic domain walls in magnetic nanowires. order of such system can be controlled by materials Magnetic domain walls are boundaries that separate engineering of the bilayer system owing to the inter- regions magnetized in different directions. The moti- facial anti-symmetric exchange interaction known as vation of this study is to build the Racetrack Memo- the Dzyaloshinskii-Moriya interaction. These works ry proposed my supervisor Dr. Stuart Parkin. Using were published in Nature Materials and Nature nanosecond current pulses, we demonstrated in-sync Communications in 2013, 2014. motion of multiple domain walls. The direction to which the domain walls moved was against the current flow, consistent with the theory of spin transfer Progress in Research torque. This work was press released by IBM and Three years have passed since I received the Sir was published in the journal of Science in 2008. Martin Wood Prize and significant advances are The use of spin polarized current to manipulate made in many areas of the field. The combination magnetization triggered efforts to develop means of of spin current generation from the spin Hall effect magnetization control in a more efficient way. Of and the chiral magnetic order via the Dzyaloshin- particular interest was the use of "spin current". Spin skii-Moriya interaction has led to findings of hetero- current consists of electrons possessing opposite structures that enable fast motion of domain walls spins moving in opposite direction and is considered and is being applied for the Racetrack memory tech- to provide technologically viable approaches to con- nology. On a similar line, the chiral magnetic order trolling magnetization. is now utilized to generate skyrmions, a topological

60 20 years of the Millennium Science Forum object that can also be used to construct Racetrack photon/spin interface can be applied to quantum in- memory. Current induced motion of skyrmions has formation technologies, solid understanding on the been observed and various approaches to controlling coupling between the two is needed which we hope the topological object have been proposed and are to provide in the near future. now being experimentally verified. On the front of generating spin current or local spin density known as "spin accumulation", interest has been shifted Reflections from the elements in the periodic table to alloys and Congratulations to the Sir Martin Wood Prize for multilayers. Of particular interests are the topolog- its 20th anniversary! It is simply a great honour to ical insulators, whose surfaces allow generation of be awarded this prize as a scientist in the field of giant spin accumulation. Indeed, recent reports have condensed matter physics. Personally, I would like shown that the current density needed to control the to thank the Millennium Science Forum and Oxford magnetization of an adjacent magnetic layer can Instruments for their support and providing me an be orders of magnitude smaller when topological opportunity to meet many people around the world. insulators are used instead of the conventional para- I am also very grateful to Sir Martin and Audrey magnetic heavy metal. Although the mechanism of Wood for their hospitality and their time for show- how spin current/spin accumulation is created at the ing me the history of superconducting magnets and interface is under debate, the uniqueness of the elec- Oxford Instruments. Perhaps the uniqueness of this tronic state of topological insulators may continue to award is also due to the selection committee who, stimulate research for the coming years. I heard, vigorously discuss the nominees’ research We have been working on various material systems each year to decide the awardee. and approaches to control the spin orbit interaction of My visit to Stuttgart and the UK was an exception- thin film heterostructures and explore the fascinating al event that I will remember till I lay in my grave. physics that may arise. The large spin current gener- I thank Professor Takagi for inviting me to the MPI ated from the large spin orbit coupling of the mate- at Stuttgart: I vividly remember the discussions (not rial can in turn influence its resistivity. Such effect, particularly related to science) we had in his office. known as the spin Hall magnetoresistance, provides It was inspiring to travel around and see the history means to characterize the size of spin current gen- of Oxford and other cities in the UK. The muscle erated from the spin Hall effect and others. We have men winding the superconducting wires around a used this approach to study the spin Hall effect of tiny bobbin at Oxford Instruments was one of the the early 5d transition metals (with near amorphous highlights of the trip. But without Tony Ford and Dr. structure) and found the conductivity of the spin Dinah Parker, I would have been lost somewhere in current generated via the spin Hall effect depends the middle and I would like to thank their support on the number of 5d electrons. These results suggest throughout my trip. that the spin Hall effect of the early 5d transition metals originates from the unique band structure of each element, which is known as the intrinsic contribution to the spin Hall effect. Applying the concept of spin Hall magnetoresistance, we have succeeded in observing the direct conversion of heat current to spin current, often referred to as the spin Nernst effect, in tungsten. We find that the efficiency of heat Lecture Trip to spin conversion is similar to that of current to spin Max Planck Institutes Stuttgart, University of Ox- conversion. ford, Imperial College London, University of Cam- bridge, University of York More recently, we have been working on the forefront of photon-spin coupling, where we use circularly and/or linearly polarized light to probe Contact Information [email protected] and control the electrons’ spin orientation. As the

20 years of the Millennium Science Forum 61 Winner in 2015

Current title and affiliation Associate Professor, Department of Physics, Takuya Satoh Faculty of Science, Kyushu University

1998: B.Eng. Department of Applied Physics, The University of Tokyo 2000: M.Eng. Department of Applied Physics, The University of Tokyo 2004: Ph.D. Department of Applied Physics, The University of Tokyo 2003-2005: Research Fellow, Max Born Institute, Germany 2006-2007: JST Research Fellow, The University of Tokyo 2007-2014: Assistant Professor, Institute of Industrial Science, The University of Tokyo 2010-2014: JST-PRESTO Researcher 2014-Present: Associate Professor, Department of Physics, Kyushu University Generation and control of magnetic excitations by polarized light in antiferromagnets and ferrimagnets Title and affiliation when prize awarded Associate Professor, Department of Physics, Faculty of Science, Kyushu University We also demonstrated, for the first time, time and Abstract when prize awarded phase resolved imaging of spin wave propagation in The interaction between light and magnetism is con- a ferrimagnet induced via the inverse Faraday effect. sidered a promising route to the development of en- It was shown that the wave number distribution of ergy-efficient data storage technologies. The Faraday the excited spin wave is proportional to the frequen- effect is a well-known magneto-optical effect. Line- cy component of spatial spot of the excitation beam. arly polarised light passing in the direction parallel This fact led to the directional control of spin wave to the magnetisation is subject to Faraday rotation. propagation, thus demonstrating spin wave manipu- In this effect, we can say that magnetism acts on lation by using spatially shaped optical pulses. light. There is also an inverse effect; namely, where Finally, we have demonstrated the one-to-one trans- light acts on magnetism. The inverse Faraday effect fer of the polarisation eigenstates of a fully polarised is where circularly polarised light generates an ef- pump light wave onto the magnetic eigenmodes of a fective magnetic field. Conversely, linearly polarised three-sublattice antiferromagnet. We converted the light passing in the direction perpendicular to the magnetic information back into the optical polarisa- magnetisation is subject to magnetic birefringence. tion eigenstate of a probe light wave in an equally This is called the Cotton-Mouton effect, which is a one-to-one process. second-order magneto-optical effect. The inverse These results will pave the way for new fields of Cotton-Mouton effect is where linearly polarized “terahertz-spintronics” and “optomagnonics” for light generates an effective magnetic field. These generating and controlling magnetic excitations by inverse magneto-optical effects have been used for polarised light. non-thermal optical excitation of spin oscillations in (weak)ferromagnets. The resonance frequency of spin oscillation in antiferromagnets is extremely high due to the exchange interaction between adjacent spins, and faster magnetisation control had been expected. However, it was believed that the inverse Faraday effect does not act on pure antiferromagnets with zero net magnetisation. Optical control of antiferromagnets had not been reported. We succeeded in excitation of spin oscillation in NiO by illuminating circularly polarised light pulses and in optical control of antiferro- Fig.1:Schematic for propagation of spin waves excited by fem- magnets. tosecond laser pulses.

62 20 years of the Millennium Science Forum Kurosawa for arranging everything as a secretariat. Progress in Research And finally, I would like to give special thanks to Terahertz spintronics Tony Ford for his tremendous effort in arranging Antiferromagnetic materials are nowadays studied the lecture tour. During the time I spent with Tony, I more extensively in view of terahertz magnetisation learnt about the British culture from him. control using femtosecond laser pulses as well as terahertz magnetic field pulses. Nonlinear excitation of magnetization leading to magnon-magnon and magnon-phonon interactions, and its relaxation are important subjects. Furthermore, coherent and ultrafast spin manipulation/magnetization reversal with shaped pulses will be investigated.

Optomagnonics In our technique, neither microwaves nor spin-polarized current are used at all; the spin wave is generated and directed only by the spatially shaped light pulse. We expect that our technique will allow Fig.2: Two-dimensional maps of spin-wave emission. much higher design flexibility in magnonics, and that this technique will pave the way for a new field of "optomagnonics" for manipulating spin waves with light spots of various shapes. We will work on spatial light modulation using computer generated holograms toward arbitrary tuning of the spin wave propagation.

Reflections Hearty congratulations for the 20th anniversary of the Sir Martin Wood Prize. I feel very honored to be Fig.3: Lecture at the University of York one of the recipients of the Sir Martin Wood Prize. It is surely a great opportunity and a gift of encouragement to my career. The lecture tour was truly exceptional, it was really a once-in-a-lifetime experience for me. The experience will be appreciated in my mind for a long time. I still keep in touch with people who I met on the tour, and will develop future relationships between the UK, Germany, and Japan. I sincerely thank Sir Martin Wood, Professor Nob- oru Miura, Professor Maki Kawai, Mr. Kitaura, Mr. Watanabe, Sir Peter Williams and all the steering committee members of the Millennium Science Lecture Trip Forum, Professor Hidetoshi Fukuyama, Professor Max Planck Institutes Stuttgart, University of Ox- ford, University of Exeter, University of York Hidenori Takagi and all the Prize Selection Commit- tee members, the British Embassy in Japan, Japanese embassy in the UK, and people from Oxford Instru- Contact Information [email protected] ments in Japan and the UK. I am grateful to Hidemi

20 years of the Millennium Science Forum 63 Winner in 2016

Current title and affiliation Professor, Institute for Molecular Science, Na- Akihito Ishizaki tional Institutes of Natural Sciences

2001: B.S., Faculty of Science, Kyoto University 2008: D.Sc., Department of Chemistry, Kyoto University 2008-2010: Japan Society for the Promotion of Science Postdoctoral Fellow for Research Abroad, University of California, Berkeley (USA) 2010-2012: Postdoctoral fellow, Lawrence Berkeley National Laboratory (USA) 2012-2016: Research Associate Professor, Institute for Molecular Science 2016-present: Professor, Institute for Molecular Science 2016-present: Professor, School of Physical Sciences, Graduate University for Advanced Studies Theory of real-time quantum dissipative dynamics and its application to photosynthetic light harvesting systems Title and affiliation when prize awarded Professor, Institute for Molecular Science

ergy characterising pigment-protein coupling and Abstract when prize awarded excitonic coupling between pigments. In our work, Essentially, a quantum system never can be regard- however, the main stress fell on the fact that the na- ed as an isolated system. Quantum systems are ture of the energy transfer is also dominated by the always in contact with “the outside world.” Hence mutual relation between two timescales, the protein their quantum natures are sometimes sustained and reorganisation time and the inverse of the excitonic sometimes destroyed. In condensed phase molecular coupling. Considerations about the finite timescale systems, especially, quantum systems are affected by effects of protein-induced fluctuation-dissipation a huge number of dynamic degrees of freedom, such led to the rigorous theoretical framework describing as solvent molecules, amino acid residues in pro- photosynthetic energy transfer. As a consequence, teins, and so forth. Balance between robustness and we revealed that the photosynthetic energy transfer fragility of the quantum natures may dramatically process is well-optimised in the parameter region alter behaviours of chemical and biophysical dynam- corresponding to nature by utilising a fine balance ics. On the experimental side, it has become possi- between the quantum mechanical delocalising ef- ble to explore molecular processes on a timescale fect and the protein-induced localising effect of the down to femtoseconds by means of ultrashort laser electronic excitations. A series of our papers was pulses. This progress in spectroscopy has opened up not only well accepted in the community of pho- real-time observation of dynamic processes in com- tosynthetic research, but also stimulated a burst of plex molecular systems and has provided a strong activity among multidisciplinary communities, such impetus to theoretical studies of real-time quantum as condensed phase chemical physics and quantum dissipative dynamics. physics. Investigation on the primary steps of photosynthesis is an example of such efforts. Photosynthetic energy conversion starts with the absorption of a photon of Progress in Research sunlight by one of the light-harvesting pigments, fol- By taking advantage of insights and theoretical tech- lowed by the transfer of electronic excitation energy niques obtained from photosynthetic research, we to the reaction centre. Ultrashort timescales of pho- have been investigating artificial systems such as tosynthetic energy transfer require that all the rele- organic photovoltaic systems. Organic photovoltaic vant timescales in the problem be self-consistently systems consist of a blend of donor and acceptor included in any physical model that attempts to elu- organic materials, and the photogenerated molecu- cidate the mechanisms. Ordinarily, photosynthetic lar exciton in the donor domain would dissociate at energy transfer is discussed in terms of the mutual the donor/acceptor heterojunction into a hole and relation between magnitudes of reorganisation en- electron. Subsequently, the electron and hole would

64 20 years of the Millennium Science Forum separate into free charge carriers to be extracted as strongly suppresses the electron transfer reaction to photocurrents. In efficient organic photovoltaic ma- the interfacial charge transfer state stabilised at the terials, the electron and hole escape from the hetero- donor/accepter interface and plays a critical role for junction and long-range charge separation proceeds maintaining the long-range electron-hole separation. efficiently.

However, a question naturally arises concerning Reflections the physical mechanism of the long-range charge I would like to express my sincere gratitude and separation process. This is because the electron and congratulations on the 20th anniversary of the Sir hole are subject to their mutual Coulomb attraction, Martin Wood Prize. Although I was awarded the hence they might be thought to relax to a bound 18th Sir Martin Wood Prize, it is my great honor electron-hole pair localised at the interface. The re- to be the 20th awardee. Last year, I had invaluable combination of the once-separated electron and hole experiences on the Sir Martin Wood Prize lecture is a major loss mechanism in photovoltaic systems tour in Germany and the UK; it is still as fresh in my that control their performance. Hence, it is the key to mind as if it had happened yesterday. In particular, elucidate physical mechanisms of how the electron I feel a great sense of gratitude to Sir Martin Wood and hole escape from the donor/acceptor interface and his wife, Audrey, as well as Professor Hidenori for understanding the crucial factors determining the Takagi of Max-Planck Institute Stuttgart and Dr energy conversion efficiency of organic solar cells. Michael Cuthbert of Oxford Instruments for their Furthermore, from the standpoint of fundamental heart-warming hospitality. Certainly, the invaluable physics, it can be said that great strides in the devel- and memorable journey was impossible without opment of organic solar cells have posed fundamen- Tony Ford and Hidemi Kurosawa, who made exten- tal physical problems regarding quantum dynamical sive arrangements. I would like to express my cor- phenomena related to exciton and charge generation dial gratitude to them, too. and transport in complex molecular systems. I was very surprised to be selected as the Sir Martin Recently, we theoretically proposed a “non-Mark- Wood Prize winner in 2016, because my research ovian quantum-classical ratchet mechanism” made area of condensed phase quantum and chemical dy- possible via the combination of quantum delocal- namics was considerably different from those of the isation and its decoherence, to get insight into the former prominent awardees selected from the field inner working of experimentally observed ultrafast of condensed matter physics. I am grateful for the long-range charge separation and protection against broadness of themes covered by the Sir Martin Wood the charge recombination at the donor/acceptor in- Prize. I believe it represents the open-mindedness of terface. Our theoretical and computational results the selection and steering committees in accepting revealed the following steps enabling the ratchet heterogenous material. I believe this open-minded mechanism: (1) The electron travels using quan- prize will continue to stimulate younger researchers tum delocalisation, straddling multiple molecules, of condensed matter science and to encourage fur- leading to the fast and long-range forward electron ther growth of the research fields. transfer. (2) Subsequently, the small polaron formation induces decoherence to localise the product state. This time-lagged decoherence is crucial because the quantum delocalisation would allow facile Lecture Trip backward transfer away from the product state. (3) Max Planck Institute Stuttgart, University of Ox- Then, the backward electron transfer is suppressed ford, University College London, University of Manchester, University of Leeds because it requires incoherent hopping that needs to overcome free energy barriers. Specifically, it was revealed that the non-Markovian effect—originated Contact Information [email protected] from slow timescales of the polaron formation—

20 years of the Millennium Science Forum 65 Winner in 2017

Current title and affiliation Associate Professor Quantum-Phase Electronic Michihisa Yamamoto Center, The University of Tokyo, Unit Leader, RIKEN Center of Emergent Matters, RIKEN

Michihisa Yamamoto was born in Shizuoka prefecture, Japan in 1976. He received his B. Sc. (1999), M. Sc. (2001), and Ph.D. (2004) in physics from the University of Tokyo. He was a research Associ- ate Professor (2004-2014) and a lecturer (2014-2017) in the Department of Applied Physics and an Associate Professor (2017-2018) in Quantum-Phase Electronics Center at the University of Tokyo. Since 2017, he is a unit leader at RIKEN Center for Emergent Matter Science.

Measurement and control of the phase of an electron wave Title and affiliation when prize awarded Associate Professor Quantum-Phase Electronic Center, The University of Tokyo

tunnelling of an electron between the two paths. Abstract when prize awarded Adjusting the tunnel coupling energy, we can moni- The phase of a wave function is the most funda- tor and suppress the contribution of encircling paths mental concept of quantum mechanics. Among a while keeping the large AB oscillation amplitude. variety of interference phenomena that can reveal This solid-state analogue of the double-slit experi- this quantum phase, a two-path interference is the ment allows for measurement and control of the true simplest. Consequently, the Aharonov-Bohm (AB) transmission phase shift of an electron. interferometer, which is usually considered as a two- path interferometer, has been the most popular play- We applied this phase measurement technique to ground for physicists. In the AB interferometer, the investigate the scattering of an electron wave by an relative transmission phase between the two paths artificial atom. We embedded a quantum dot into can be controlled by external magnetic field B. This one of the two paths of the interferometer to meas- phase difference causes an oscillation of the current ure the scattering phase through an artificial atom. In as a function of B. It turned out, however, that the addition to the Friedel sum rule, which connects the two-terminal linear conductance through an AB ring number of electrons in the quantum dot to the scat- suffers from the so-called phase rigidity. tering phase, we have revealed influences of the parity of orbital wave function and the interaction be- Onsager’s law for linear conductance, G(B)=G(-B), tween a local spin confined in the quantum dot and implies that the phase of the AB oscillation can only conducting electrons in the reservoirs, i.e. the Kondo take the values 0 or π at B = 0. To satisfy this bound- effect. In particular, we observed π/2 phase shift in ary condition, contribution from paths of an electron the Kondo regime as the hallmark of the Kondo ef- encircling the AB ring multiple times needs to be fect, interpreted as the fingerprint of local moment added. What is usually observed in an AB experi- screening. ment is therefore not an ideal two-path interference. Using multi-terminal as well as multi-channel AB interferometers, numerous attempts have been made Progress in Research to measure and control the phase shift of an electron I am extending the concept of “quantum electron wave, however, no reliable phase measurement had wave technology” (citation of the award). I plan to been realised. use a special kind of quasi-particles, which are defined as elementary excitation of correlated states In this work, we showed that a pure two-path inter- that can travel over macroscopic distance without ference is realised by combining the AB ring with suffering from decoherence, as information carriers parallel tunnel-coupled quantum wires that allow on quantum electron waves. In addition, I am trying

66 20 years of the Millennium Science Forum to use “standing waves” to detect finite size effects number of misled people; we sometimes got aggres- of quantum systems. My recent research involves sively negative referee comments when we submit- using two-dimensional layer materials such as ted papers. Also, as the theoretical work has largely graphene and transition metal dichalcogenide. I am been established and our experiments were quite also starting up a new laboratory in RIKEN. conclusive, we could not expect a good “citation number” in the short-term. Apart from our absolute confidence in what we were Reflections doing, our motivation was that we wanted simply to I felt extremely honoured when I was awarded the know the truth and see the view from the top in this Sir Martin Wood Prize. Honestly speaking, it was fundamental issue; we expected to see and open up more than I expected. I appreciate very much that something very new and fundamental. I believe that the selection committee evaluated highly my work this kind of motivation is more important than hop- on the measurement and control of the phase of an ing to get a good reputation by simply following a electron wave. For the purpose of young researchers, short-term trend. in particular, I would like to describe how I could achieve it. Measurement and control of the phase is a very well-known, long-term and fundamental problem. I believe that, about 20 years ago, most researchers who had nanofabrication and low temperature measurement facilities were making some attempts at it. Despite a lot of efforts by many people, nobody could do it, although some researchers claimed that they could. Their results were inconsistent with theories, even at very fundamental stages. On the other hand, efforts made in these previous works were indeed significant. Some employed very complicated device structures as well as the most advanced measurement skills. Researchers therefore claimed that they did the best imagined in the world and that inconsistency with theories indicates that those theories overlook something. With such a message delivered to the community, many people were misled that the problem was at least experimentally solved. This was the situation when I conceived and started this project. I had to start by convincing people in my own group that the problem had not at all been solved experimentally. Once I obtained promising data, my supervisor, Professor Seigo Tarucha gave me significant support and encouragement. Then the number of people involved increased; I was joined by Dr Shintaro Lecture Trip Takada and Dr Christopher Bäuerle, without whom Max Planck Institute Stuttgart, University of Cam- I believe I could never have gained such a great bridge, University of Oxford, University of Man- chester, University College, London achievement. All those involved really liked the project and became highly motivated and excited. But there were also some risks. First, the work was Contact Information [email protected] not so easy, particularly in the beginning, due to the

20 years of the Millennium Science Forum 67 Winner in 2018

Current title and affiliation Associate Professor, Department of Applied Yoshihiko Okamoto Physics, Nagoya University

2001: B.S. Department of Applied Chemistry, The University of Tokyo 2003: M.S. Department of Advanced Materials Science, The University of Tokyo 2006: Ph.D. Department of Advanced Materials Science, The University of Tokyo 2006: Special Postdoctoral Researcher, RIKEN 2006-2014: Research Associate, Institute for Solid State Physics, The University of Tokyo 2014-present: Associate Professor, Department of Applied Physics, Nagoya University 2014-2018: Associate Professor, Institute for Advanced Research, Nagoya University

Exploration of Novel Physical Properties and Functions of Transition Metal Compounds Based on the Unique Electronic and Crystal Structures

at room temperature, indicating that Ta4SiTe4 is a Abstract when prize awarded promising candidate for the low temperature appli- Novel transition metal compounds with remarka- cations of thermoelectric cooling. This very large P ble electronic properties, such as cuprate and iron- is probably caused by the very small spin-orbit gap based superconductors, have opened up a new era opening on the strongly one-dimensional electronic of the condensed matter physics. In my Sir Martin bands at the Fermi energy. Wood Prize lecture I will present the results of material exploration of transition metal compounds 2. CaAgP and CaAgAs as a candidate nodal-line using the crystal and electronic structure databases semimetal. based on knowledge of solid state chemistry, to- In recent years, Dirac and Weyl semimetals, which ward the discovery of such electronic properties and are zero-gap semiconductors with linear dispersion functions. We developed various materials including bands at the zero-gap points, have attracted broad high-performance thermoelectric materials, candi- interest as candidate systems for realizing topologi- date nodal-line semimetals, metal-insulator transi- cally nontrivial states in bulk materials. In contrast, tion systems, superconductors, and geometrically some systems are theoretically indicated to have a frustrated magnets and I will focus on the former nodal line, where the linear dispersion bands cross two systems. on a line in the momentum space. We found that CaAgP and CaAgAs are promising candidates for

1. One-dimensional telluride Ta4SiTe4 as a high the nodal-line semimetal. First principles calculation performance thermoelectric material. results indicate that the both compounds are ideal Thermoelectric cooling is a promising candidate nodal-line semimetals, where the Dirac points form for the next-generation of refrigeration technologies a ring at the Fermi energy. We synthesized polycrys- in replacing vapor compression cooling using gase- talline samples and single crystals of CaAgP and ous refrigerants. However, there is currently no bulk CaAgAs and found that they have a ring-torus Fermi material with a high enough performance to reach surface related to the nodal ring by physical property a practical level in the low temperature region. We measurements of them. found that Ta4SiTe4 and its substituted compounds show high thermoelectric performance at low temperature. Thermoelectric power of Ta4SiTe4 whisker Reflections crystals reaches S = -400 μV K-1 at 100-200 K, while It is great honor for me to receive the Sir Martin maintaining low resistivity of ρ ~ 2 mΩ cm. These S Wood Prize. I have been exploring novel transition and ρ give a larger power factor of P = S2/ρ of 80 μW metal compounds since I was a graduate student. I -1 -2 cm K than those in Bi2Te3-based practical materials was thinking how I can contribute to the progress of

68 20 years of the Millennium Science Forum condensed matter physics, although I have a back- recognizing my work. Another great thing about a ground of chemistry. I can neither develop a theory material exploration study is that one can directly by using complex mathematical formulae nor con- collaborate with many experimentalists and theorists duct sophisticated physical property experiments through the novel materials. My study is supported based on the latest finding in physics. However, I by many of these collaborators. I would like to thank could find various interesting materials and make many people including the collaborators, my super- them visible to physicists by using my knowledge visors, staff of our department, and present and past of solid state chemistry. I was unsure whether this members of our research group. method has scientific significance, but this award gives me confidence and I’m grateful to commit- Contact Information tee members of the Millennium Science Forum [email protected] and Sir Martin Wood Prize selection committee for

Prize Selection Committee Meeting

The Nomination period for the 2018 Sir Martin Wood Prize was from 1st April to 1st August 2018. The prize selection committee met on 2nd September 2018 (below) and chose Dr. Yoshihiko Yamamoto as the winner.

20 years of the Millennium Science Forum 69 Sir Martin Wood Prize Winners 1999 – 2018

In alphabetical order

Awarded Family name First name year Current title and affiliation Associate Professor, Department of Applied Physics, The University of Chiba Daichi 2012 Tokyo Fujisawa Toshimasa 2003 Professor, Department of Physics, Tokyo Institute of Technology Associate Professor, Department of Physics, The University of Tokyo & Hayashi Masamitsu 2014 Group leader, Spin Physics Group, National Institute for Materials Science Professor, Institute for Molecular Science, National Institutes of Natural Ishizaki Akihito 2016 Sciences Associate Professor, Laboratory for Future Interdisciplinary Research of Kawano Yukio 2011 Science and Technology, Tokyo Institute of Technology Professor, Graduate School of Frontier Sciences, The University of To- Kimura Tsuyoshi 2005 kyo Chief Scientist, Director of Surface and Interface Science Laboratory, Kim Yousoo 2009 RIKEN Kizuka Tokushi 2000 Professor, Department of Materials Science, University of Tsukuba Professor, Department of Physics, Tokyo Institute of Technology PRES- Murakami Shuichi 2010 TO, Japan Science and Technology Agency Professor, Research Center for Advanced Science and Technology, The Univer- Nakamura Yasunobu 1999 sity of Tokyo, Team Leader, Center for Emergent Matter Science, RIKEN Ohno Yuzo 2004 Professor, Faculty of Pure and Applied Sciences, University of Tsukuba Professor, Department of Chemical Science and Engineering, Tokyo In- Ohtomo Akira 2007 stitute of Technology Okamoto Yoshihiko 2018 Associate Professor, Department of Applied Physics, Nagoya University

Ono Teruo 2008 Professor, Institute for Chemical Research, Kyoto University Associate Professor, Department of Physics, Faculty of Science, Ky- Satoh Takuya 2015 ushu University Saitoh Eiji 2008 Professor, Department of Applied Physics, The University of Tokyo Professor, Institute of Engineering Innovation, School of Engineering, Shibata Naoya 2013 The University of Tokyo Professor, Division of Materials Physics, Graduate School of Engineer- Shimizu Katsuya 2000 ing Science, Osaka University Shirahama Keiya 2001 Professor, Department of Physics, Keio University Prime senior researcher : National Institute of Advanced Industrial Sci- Suenaga Kazutomo 2006 ence and Technologies Terasaki Ichiro 2002 Professor, Department of Physics, Nagoya University Associate Professor Quantum-Phase Electronic Center, The University Yamamoto Michihisa 2017 of Tokyo, Unit Leader, RIKEN Center of Emergent Matters, RIKEN

70 20 years of the Millennium Science Forum Appendix

20 years of the Millennium Science Forum 71 Prize Ceremony Memories

HRH The Princess Royal awards the 1999 Millennium Science Forum Honorary Prize to Hiroshi Yasuoka

1999 Millennium Science Forum Honorary Prize Sir Martin awards the 1999 1st Prize to Yasunobu winner Hiroshi Yasuoka Nakamura

2000 joint 2nd Prize winners Tokushi Kizuka and Sir Martin awards the 2001 3rd Prize to Keiya Katsuya Shimizu Shirahama

Sir Martin awards the 2002 4th Prize to Ichiro 2003 Guest speaker Professor Robin Nicholas, Terasaki University of Oxford

72 20 years of the Millennium Science Forum Sir Martin awards the 2003 5th Prize to Toshimasa Fujisawa

2002 Guest speaker Professor Sir Harold Kroto, University of Sussex

Sir Martin awards the 2004 6th Prize to Yuzo Ohno Sir Martin awards the 2005 7th Prize to Tsuyoshi Kimura

Sir Martin awards the 2006 8th Prize to Kazutomo Sir Graham Fry, UK Ambassador, awards the 2007 Suenaga 9th Prize to Akira Ohtomo

Sir Martin and Sir David Warren, UK Ambassador, award Sir David Warren, UK Ambassador, awards the the 2008 joint 10th Prize to Teruo Ono and Eiji Saitoh 2009 11th Prize to Yousoo Kim

20 years of the Millennium Science Forum 73 Prize Ceremony Memories

Sir Martin awards the 2010 12th Prize to Shuichi Sir David Warren, UK Ambassador, awards the Murakami 2011 13th Prize to Yukio Kawano

Sir Tim Hitchens, UK Ambassador, awards the Julia Longbottom, UK Minister, awards the 2012 2013 15th Prize to Naoya Shibata 14th Prize to Daichi Chiba

2012 Guest speaker Professor Professor Fukuyama and Professor Miura with Sir Martin Wood Prize Alumni (2012) Koichi Kitazawa, President, JST

2014 Guest speaker, Dr. Julie Maxton, Executive Sir Tim Hitchens, UK Ambassador, awards the Director, The Royal Society 2014 16th Prize to Masamitsu Hayashi

74 20 years of the Millennium Science Forum Sir Tim Hitchens, UK Ambassador, awards Takuya Satoh giving the prize lecture the 2015 17th Prize to Takuya Satoh

Sir Tim Hitchens, UK Ambassador, awards the Paul Madden, UK Ambassador, awards the 2017 2016 18th Prize to Akihito Ishizaki 19th Prize to Michihisa Yamamoto

Delegates at the 2017 MSF at the courtyard of the British ambassador's residence in Tokyo

20 years of the Millennium Science Forum 75 Record of the MSF

Steering Committee and Selection Committee members

MSF Steering Com- Sir Martin Wood Prize Affiliation when appointed MSF Committee mittee Selection Committee Noboru Miura The University of Tokyo 1999-2006 2007- Hidetoshi Fukuyama The University of Tokyo 1999-2006 2007- Koichi Katsumata RIKEN 1999-2003 Koichi Kitazawa The University of Tokyo 1999-2006 2007-2014 Yasuo Endoh Tohoku University 1999-2006 2007- Toshizo Fujita Hiroshima University 1999-2003 Tomoji Kawai Osaka University 1999-2006 2007-2009 Seigo Tarucha The University of Tokyo 2003-2006 2007-2009 Yoshinori Tokura The University of Tokyo 2003-2006 2007-2009 Akira Tonomura Hitachi Ltd 2007-2012 Hideo Ohno Tohoku University 2007-2017 Yoshio Kitaoka Osaka University 2007-2014 Kazumasa Miyake Osaka University 2007-2010 Hayao Kobayashi IMS 2007-2009 Maki Kawai The University of Tokyo 2008- Yoshio Nishimura JASTJ 2008-2015 Jiro Kitaura Rigaku 2010- Hideaki Takayanagi Tokyo University of Science 2010-2014 Reizo Kato RIKEN 2010- Hidenori Takagi The University of Tokyo 2010- Masashi Kawasaki The University of Tokyo 2010- Mariko Takahashi The Asahi Shimbun 2011- Naoto Nagaosa The University of Tokyo 2011- Robin Nicholas University of Oxford 2013- Sir Peter Williams The Royal Society 2014- Kiyoyuki Terakura AIST 2015-2016 Hideo Hosono Tokyo Institute of Technology 2015- Kiyoshi Watanabe Oxford Instruments Japan 2016- Shinji Tsuneyuki The University of Tokyo 2017- Koki Takanashi Tohoku University 2018-

76 20 years of the Millennium Science Forum Guest Speakers at the Millennium Science Forum

The title is as was at that time. The MSF was held twice in 1999. 1st 1999 Spring Shunichi Kobayashi, President, RIKEN Sir Peter Williams, Former Chairman, Oxford Instruments 2nd 1999 Autumn Akito Arima, Member of the House of Councilors Sir Martin Wood, Founder, Oxford Instruments 3rd 2000 Leona Ezaki, President, Shibaura Institute of Technology 4th 2001 Mamoru Mori, Director, National Museum of Emerging Science and Innovation Lord Robert May, Professor, University of Oxford 5th 2002 Jyunjiro Kanemori, Director, International Institute for Advanced Studies Sir Harold Kroto, Professor, University of Sussex 6th 2003 Sumio Iijima, Professor, Meijo University Robin Nicholas, Professor, University of Oxford 7th 2004 Akira Tonomura, Fellow, Hitachi Ltd. Lord Robert May, Professor, University of Oxford 8th 2005 Shoji Tanaka, Director General, ISTEC Superconductivity Research Laboratory Laurence Eaves, Professor, University of Nottingham 9th 2006 Maki Kawai, Professor, The University of Tokyo Martyn Chamberlain, Professor, Durham University 10th 2007 Kiyoshi Kurokawa, Professor, National Graduate Institute for Policy Studies Maurice Skolnick, Professor, University of Sheffield 11th 2008 Michael Brady, Professor, University of Oxford 12th 2009 Sukekatsu Ushioda, President, NIMS Stephen Holloway, Professor, University of Liverpool 13th 2010 Hideo Hosono, Professor, Tokyo Institute of Technology Tomas Jungwirth, Professor, University of Nottingham 14th 2011 Tsuneya Ando, Professor, Tokyo Institute of Technology Anthony Cheetham, Professor, University of Cambridge 15th 2012 Koichi Kitazawa, President, JST Robin Nicholas, Professor, University of Oxford 16th 2013 Seigo Tarucha, Professor, The University of Tokyo Sir Peter Williams, Former Chairman, Oxford Instruments 17th 2014 Akira Fujishima, President, Tokyo University of Science Dr. Julie Maxton, Executive Director, The Royal Society 18th 2015 Masaki Takata, Professor, Tohoku University Kevin O’Grady, Professor, University of York 19th 2016 Kohzo Ito, Professor, The University of Tokyo Chris Done, Professor, Durham University 20th 2017 Eleanor Campbell, Professor, University of Edinburgh Griff Jones, First Secretary Science & Innovation, British Embassy, Tokyo 21st 2018 Motoko Kotani, Professor Tohoku University Atsufumi Hirohata, Professor, University of York

20 years of the Millennium Science Forum 77 20 years of the Millennium Science Forum -Attainments of Sir Martin Wood Prize Winners-

Editorial Committee: Kiyoshi Watanabe (Editor-in-Chief) Mariko Takahashi (Deputy Editor) Hidetoshi Fukuyama Maki Kawai Jiro Kitaura Yasunobu Nakamura Keiya Shirahama Yousoo Kim Yukio Kawano Naoya Shibata Editorial Staff: Tony Ford Kaori Oshima Production Design: Career Consulting KK Jungo Sasaki Emi Yamaguchi

This publication is supported by Oxford Instruments KK.

The Secretariat, The Millennium Science Forum TEL:+81-3-6732-8966 E-mail:[email protected]

ミレニアム・サイエンス・フォーラム事務局 TEL:03-6732-8966