- This is always the first question in my interviews for the CMD newsletter. Can you summarize your scientific trajectory? Which are your main research achievements? My scientific career probably began in pre-school age, when I earned my first pocket money by helping my father to add up columns of numbers. Mathematics was my strength and in elementary school, where four grades were taught at the same time in one classroom, I was asked by the teacher to solve the mathematical problems of the higher grades. So it was clear to me that I wanted to study mathematics. But only six months after starting my studies at the Technical University of Braunschweig, I realized that a practical application of mathematics in physics is much more interesting than pure dry mathematics, and so I ended up in physics, especially semiconductor physics, which was the most modern topic in physics at this time. Braunschweig played a very special role in my scientific career because I regularly worked in the semester breaks at the metrology institute there, the Physikalisch Technische Bundesanstalt, and thus became familiar with high-precision measurements in a wide variety of fields, including high-precision measurements of electrical resistances. There I also met my mentor Gottfried Landwehr, who dealt with low-temperature physics, superconductivity and semiconductors in strong magnetic fields. I did my doctorate and habilitation with him in Würzburg and learned infrared spectroscopy as a post-doc in the group of Tony Stradling in Oxford. Research stays at the Boltzmann Institute in Vienna and at the École Normale Supérieur in Paris extended my portfolio in semiconductor metrology to include time-resolved and microwave methods. A turning point in my scientific career was initiated by my experimental observation that the electrical resistance of a tellurium sample can be drastically changed by different etching processes. This is how I entered the field of semiconductor physics at interfaces and surfaces where two-dimensional electron gases are formed and my department at the Max Planck Institute for Solid State Research was consequently named «Low Dimensional Electron Systems». The most important scientific achievements of my team were therefore mainly in the field of quantum transport in low-dimensional electron systems with pioneering work in the field of quantum dots, electron and nuclear spin investigations in these systems as well as the discovery of novel phenomena that were recently awarded the EPS Edison Volta Prize.
- However, this is the first time that I ask the next question. You were awarded the Nobel Prize in Physics in 1985 for the discovery of the quantized Hall effect. It is common that the Nobel Prize is shared by several researchers contributing to the topic or working in the same group… can you comment on the intra-history* of your discovery? Were there theoretical predictions of the effect or you were inspired by previous work? Did you have the support of other colleagues to perform this work? (*The Spanish philosopher Unamuno introduced the concept of “intra-history” to highlight the role played by peripheral actors in History). In fact, I am the only living Nobel Prize winner in physics who received the prize unshared. Since the quantum Hall effect was a chance discovery, there was no organized team aiming at a Nobel Prize worthy goal like gravitational waves or the Higgs Boson. I was just lucky enough to discover something qualitatively new, an electrical resistance which depends exclusively on fundamental constants. Nobody expected that transport measurements on a silicon MOSFET with alloyed contacts, impurities, and undefined geometry could produce such a fundamental result. The discovery of the quantum Hall effect was purely experimental, based on the observation, that devices fabricated at different companies (Siemens and Plessey) showed small anomalies at the same value of the Hall resistance. My decision to look in more detail in this anomaly was the birth of the quantum Hall effect. This was at the high magnetic field laboratory Grenoble at 2 a.m. on the night of 4th to 5th February 1980. My experience in high precision measurements allowed me to confirm within just a few hours that the observed anomaly agreed with high precision with the fundamental resistance h/e², where h is Planck’s constant and e the elementary charge. This fact refuted the previously accepted notion that the localized electron states that exist due to unavoidable disorder in the tails of Landau levels do not influence the value of the observed Hall plateaus.
- Are there any anecdotes you can tell us about the Prize ceremony or all the fuss that came afterwards? How did this prize change your life, in a positive or negative way? The award ceremony is a very formal event with rehearsals and exact instructions on how to behave during the award presentation. Since my three children were relatively young, exact plans were made to keep my three-year-old son occupied during the award ceremony with a limousine and driver provided by the State Department and a children’s nurse so that the event would not be disrupted. However, after the press learned that my son was the youngest attendee at a Nobel Week, he had to sit in the middle of the front row in the theater with his siblings and all the television cameras focused on him, especially as he fought with his sister for the right to use the armrest. He stole the show. Since the Nobel Prize is the highest scientific award, it naturally has an influence on life afterwards. The biggest problem for all laureates is the expectation that Nobel Prize Winners should know everything and can give a competent answer to any problem, even outside their own field of work. Of course, this is not the case. On the other hand, the public has a great interest in receiving opinions on important problems from recognized scientists who are not suspected of being lobbyists. I therefore do not avoid the responsibility of taking a public position on fundamental issues. In this respect, I am involved in the issue of climate change because, as a Nobel laureate, I am a member of many scientific academies and, through contacts with high-ranking scientists, you can assess the factual situation well and, as a recognized multiplier, inform the public in an unbiased manner. In addition, photovoltaics as a subfield in condensed matter physics plays an extremely important role as a renewable energy source so I am not an outsider if I make publicity for solar energy.
- When did you find out that you were passionate about Science and/or Physics? Were you inspired by your family, teachers, books, role models or by Nature? Can you provide any advice to young students who feel the bite of Science? I already mentioned that I was interested in numbers and mathematics at a very early age. In contrast, German and foreign languages were torture for me. Parents and teachers are probably the most important people who can recognize and encourage a child’s interests. My mother, as a chemical-technical assistant, probably passed on to me an interest in the natural sciences, and my father’s profession as a forester also encouraged my curiosity to understand nature and to ask questions. However, a very important role was played by a mathematics/physics teacher in high school. He brought out my enthusiasm for these subjects and my grades in these subjects improved drastically because of this motivation. In order to encourage the commitment of teachers in science subjects, who also devote their free time to the advancement of pupils, I am the cofounder of the annual Klaus von Klitzing Prize for exceptionally engaged teachers in STEM education, which is supported by the University of Oldenburg and the EWE Foundation. If I had to give advice to young students, I would say that the most important thing is enthusiasm for the work. Also, in scientific research, internationality, cooperation and communication are very important. It is a privilege for scientists to work globally and I recommend my young scientists to change location after about 5 years to gain new experiences.
- Do you think that significant progress in Science is made by advancing small steps every day or through paradigm shifts carried out by a few geniuses? For me as an experimental physicist working in basic research, the challenge is to break new ground in small steps with the most modern instruments and measurement methods and the knowledge of experimental facts of other groups and new theoretical developments. If you are lucky, you contribute to a quantum leap. In my experimental research work I am not driven by exciting new theoretical models with the goal to be the first one to publish experimental data which may contribute to a hot topic. There is a danger of being biased in favor of the most spectacular interpretation and disregarding all other established interpretations. Unexplained experimental observations are the driving force for surprises in condensed matter physics, and it is important to have the freedom to change one’s research direction in case of unexpected observations. In this respect, I am committed to maintaining freedom in basic research, as is practiced at the Max Planck Society
- Are you in favor of syllabus at University that specializes the student in a single field, such as Physics, or the U.S. University style with major and minor degrees in more than a single field? How important is interdisciplinarity to solve the key technological problems of our society and how can we favor it? During my studies in Germany, I had the opportunity to acquire specialist skills in other areas in addition to studying physics. What is important, however, is that you acquire a deep understanding of one area and then transfer your special knowledge to another area. In this respect, interdisciplinarity is very important. To do this, however, a relationship of trust must be established between two specialists who develop visions in regular personal contacts. Communication is a success factor in solving essential problems.
- Please, tell us your opinion on what are the most exciting research topics in Condensed Matter Physics today, from your personal point-of-view. For me, two-dimensional electron systems are still the most interesting research objects in solid state physics. Quite apart from the fact that just in recent years the discovery of novel magnetic and superconducting phases in twisted bilayer graphene caused a sensation, 2-dimensional systems allow the discovery of novel physical phenomena. Only in 2-dimensional systems is it possible to study anyons in addition to bosons and fermions, which also allow access to the topological quantum computer.
- In your view, what are the challenges faced by Europe to maintain a leading position in Science and Technology with respect to U.S. and China? Can you share some piece of advice to reinforce the European position? Europe has lost weight worldwide, especially due to Brexit and too many self-interests of various states, and is not seen as a political entity. It lacks the dynamism and spirit of optimism that can be observed in China, for example. The Ukraine war was even a push to send Europe into irrelevance, to destroy the vision of a strong, united Europe. I hope that the Russian-instigated war in Europe will lead to Europe moving closer together and advocating a common strategic research and industrial policy. Europe is falling behind the world, particularly in digitization.
- In your view, how relevant are scientific associations for young and senior scientists today? What is your opinion about the European Physical Society and the European national Physical societies, compared for example to the American Physical Society? In an age of an oversupply of fake conferences, it is particularly important that scientific associations offer a wide range of serious conferences and strengthen interactions and collaborations between scientists. Since there are many strong national physical societies in Europe, the EPS, in contrast to the APS, is not viewed from the outside as an outstanding European scientific society. Here, too, Europe must grow closer together.
- Faced with a complex world, human beings tend to oversimplification. In a few short words, how would you like that future generations of Physicists remember you? I am not worried about how future generations will remember me. At least part of my scientific work has become immortal thanks to the von Klitzing constant RK=h/e² introduced worldwide as part of our international system of units with a value fixed for eternity, and that is perhaps the highest that a scientist can achieve.
- Free text…express yourself! Competition, especially in basic research, has increased to such an extent that fruitful and critical discussion of unpublished results is no longer sufficiently cultivated and the common goal of generating new knowledge is no longer in the foreground. Speculations and even fraud play an increasing role in publication submissions. Egoism is not the way to solve the great problems of mankind.
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