CERN Accelerating science

An interview with Dr. Georg Bednorz

In this interview, Dr Georg Bednorz, Nobel Prize in physics and research scientist at the IBM Zürich research center recalls the early days of this discovery and discusses future applications and challenges in the field. Earlier in autumn he was invited by the University of Geneva to give a public talk about the history of the subject -in the frame of the conference "Superconductivity: Theory and practical challenges of a quantum phenomenon"  noting that for many years it was relegated to the realm of technological utopia, since no one imagined that superconductivity could occur at anywhere near room temperature. In this interview, Dr Bednorz describes how with the discovery of new classes of superconductors these limitations are gradually being overcome, in the process revolutionizing materials science and engineering.

What drove you as a student to chemistry and latter crystallography? Could you foresee the impact that future developments in these fields would have?

During my school years, I had to take a few decisions in choosing my future career path. I was realistic enough to foresee that my marks would not allow me to become a physician because all universities had introduced limits on the number of medical students. A slight disappointment, which did not last too long because my fascination for science was growing with time. However, when I had to decide whether to continue with physics or chemistry, I decided in favour of chemistry.

The demonstration of impressive experiments and the possibility to conduct my own experiments during after hours, still under supervision, but sometimes with unexpected results, were all-important. So when I started my studies in chemistry at the university, I was full of enthusiasm. But, being unprepared for the freedom of a student’s life and just one of the hundreds of potential chemists, I soon came down to earth and really felt insecure about my future. At that time I heard about a small institute of mineralogy that was offering a geology- or crystallography-oriented curriculum and was looking for new students. I was curious to learn what they were doing, and when I asked for more information, I was impressed that I got the opportunity to talk directly to two young professors. As there were no more than a dozen students, the whole institute seemed to be more or less a family-like organization. Without hesitation, I decided to change my subject to crystallography.

Could you foresee the impact that future developments in this field would have?

As a student, I did not have the slightest idea whether that field could make significant contributions to science or technology. I simply was happy with the scientific education that taught me how to analyze the structure and properties of materials by applying the tools and methods of chemistry and physics. The truly fascinating phase came when I learned how new compounds with modified properties could be created by solid-state chemistry. Today this curriculum has developed into what is called materials science, and its impact over the years is well known.

Which do you think were the greatest influences that you had in your career?

What has been the role of family and teachers? Nobody in my family had a scientific background and, apart from forcing me to play the piano (they finally gave up after five years), my parents fully supported all my decisions with respect to my future education. My teachers, however, played a significant role in all phases of my career. In my school days, it was especially my chemistry teacher, who stimulated my interest in natural sciences and played a key role in preserving my curiosity.

Also, I should probably add that the arts teacher supported creativity. Every time someone came up with the question “Will this be possible?”, he replied with the encouraging answer: “Everything is possible”. Later, during my scientific activities, when I interacted with artists and did sculpturing myself, I still had the same response. Indeed, this has affected my attitude as a scientist so deeply that I am almost allergic to rush or sloppy statements, including the word “impossible”. As a student, I was guided by my academic teachers in my experimental activities and encouraged to take the challenge and spend a few months outside the university.

The time that I spent as a summer student at the IBM Zurich Research Laboratory was a valuable experience for me, because I could see how my scientific education could be applied in the real research environment of an industrial laboratory. In the Physics department, headed by K. Alex Muller, I worked under the guidance of H. J. Scheel, learning about different methods of crystal growth, materials characterization and solid-state chemistry. I enjoyed that even I — at the time only a student — was given the freedom to work on my own. This gave me the opportunity to make mistakes, but also to correct them and learn. Looking back, this helped me lose the fear of approaching new problems in my own way, and eventually dive into the unknown. This attitude was decisive for my scientific career.

Did you ever feel disappointment in your research career? Can we learn something from projects that have failed?

Well, there have been several disappointing events during my career. The first that I recall happened already during my Ph.D. years. Upon invitation by K. Alex Müller (at IBM) and H. Graenicher at the ETH Zurich, I started my Ph.D. thesis at the Laboratory of Solid State Physics in 1977. I gained my first experience with low-temperature experiments during my studies of structural and ferroelectric phase transitions in mixed perowskite crystals. I was fascinated by the variety of properties displayed by these compounds and how they could be changed by doping. It was only a side activity that brought me into contact with superconducting oxides: IBM’s Gerd Binnig, who would later become famous as one of the fathers of the Scanning Tunneling Microscope (STM), had earlier worked on superconducting SNx and oxygen-deficient SrTiO3 (a model perowskite), which was a superconductor at 0.3 K. He was curious to find out whether the carrier density and the Tc could be enhanced by proper doping. Doping SrTiO3 was really my specialty, and only two days after a short telephone call, I could hand over a Nb-doped SrTiO3 crystal to Gerd. This marked the beginning of a fruitful two-year collaboration.

It turned out that it was indeed possible to tune Tc by increasing the carrier density to obtain a transition temperature of 1.2 K. The optimism one could reach even higher transition temperatures with higher doping turned into disappointment when the Tc started to decrease. To make things even worse, from 1980 on Gerd Binnig concentrated his efforts on the development of the STM, so I lost my partner at IBM to continue the superconductivity project. I would not regard this project as a failure, but the involuntary termination had left its marks.

Later, it turned out to be a decisive moment for starting the new endeavor of oxide superconductivity. But before talking about this, I will address my first years after my Ph.D. In 1982, I joined the IBM Zurich Research Laboratory to work on insulating, mostly ferroelectric oxides and to investigate single crystals and ceramics.

The next step was to create a system to grow new materials in the form of thin films by sputter deposition. While the STM group was publishing the first exciting results from metal and semiconductor surfaces, the management of my group was thinking about studies of the initial stage of thin-film crystallization using the STM as analytical tool. Consequently, I was gently steered towards designing and constructing a multi-chamber vacuum system with chambers for deposition, analytical surface science tools and the STM for in-situ experiments, i.e., for analysis without breaking the vacuum. Although this was an excellent idea, and is a standard experiment nowadays, it came too early in the STM development at the time. Because of fundamental problems with the design and the electronics, the project was not suited to create satisfaction, neither for myself nor for the management. I made up my decision to somehow get out of the project. I guess both sides were happy when a new position for a new materials effort was created and I immediately jumped on the opportunity. The consequence was a new start where I would be responsible.

Could you share with us a few thoughts on the discovery of high-temperature superconductivity in ceramic materials?

There were certainly several decisive moments essential for the later success in that project. When Alex Müller approached me in 1983 and asked me whether I would join him in the search for high-temperature superconductivity in conducting oxides, I — much to his surprise — agreed immediately. It was the brief experience with Nb-doped SrTiO3 with its disappointing ending that made my decision easy. The goal of the project at that time was very ambitious, since it was against the mainstream. But the idea to involve the Jahn-Teller effect to create polarons, which could lead to a high electron-phonon interaction, was so appealing to us that we took the risk of diving into the unknown and embarking on a road of uncertainty. Our concern, however, was that specialists in the field would regard the approach as absurd, so we agreed not to talk about it to anybody else.

Karl Alexander Müller and Johannes Georg Bednorz in the IBM laboratory.  

How did you manage to keep the secret?

The consequence for me was that I did this research only part-time. While I could synthesize, characterize and prepare new compounds for resistivity measurements during the day, the resistivity measurements themselves were performed after normal office hours.

Thankfully, our colleagues working on semiconductors allowed us to use their equipment after they had left for the evening. Surprisingly, during the day, nobody noticed that many of the materials I worked with were sometimes black because they were conductors. Luckily, the idea of the Jahn-Teller effect in transition-metal ions as a guideline narrowed down the number of candidates to be investigated, but there still were plenty of possibilities. We first worked on nickel-oxide-based compounds and after a while included copper as a second Jahn-Teller ion.

For years, the resistivity showed more or less the same behavior: starting in a conducting state at room temperature and turning into an insulator when approaching He temperatures. The project entered a critical phase in 1985 with growing concern that the target we were aiming at might not exist and that possibly we had embarked on a path ending in a blind alley. Our optimism and energy had reached a low point, so from time to time, I had to take a break from the work.

What brought you out of this can we call it –depressive- mode?

Nothing, it was only the final success, the moment of the discovery. Until then, there had been no indication whether the dream would become reality.

Occasionally, I would resume my work on the subject because I did not want to accept that our approach should be completely wrong. I started to study the literature and by chance I found an article about Cu-containing conducting oxides, from which I immediately realized what I was doing wrong. I intuitively felt that this was the solution. With this new insight, it was immediately possible to find the first signs of a transition to superconductivity. Driving this transition to the new record high of 35 K was only a question modifying the chemistry. As for the discovery, I find these two quotes of Albert Szent-Gyorgyi, the discoverer of vitamin C, to be very appropriate: “A discovery is said to be an accident meeting a prepared mind.” And, concerning the article I discovered and which had been written by authors looking for catalytic properties at temperatures far above ambient: “A discovery is made by looking at the same thing as everyone else and thinking something different.”

After the discovery, we were asking ourselves how this would be received by the scientific community. There had been wrong announcements of superconductivity in the past, and we were afraid that we would have to fight for years to have our results accepted by the wider scientific community. But we were soon overwhelmed by the response that our work had within a few months.

I am sorry if I am repeating myself but could you foresee the applications that your discovery could have at that time? Were there other surprises?

First of all, Alex Müller and I were very pleased that the superconducting transition temperature could be enhanced by 50% with the oxides, as compared to the metals or alloys. However, we did not expect the dramatic developments that followed as a result of the intense worldwide research activities that started at the end of 1986.

When the barrier of 77 K had been surpassed, it was difficult to refrain from joining in the enthusiastic predictions by scientists and the media that many applications, most prominently the transport of energy, would be realized within a few years. I recall the advice of one of my IBM colleagues to never lean out too far and make the mistake of emphasizing the potential use for transporting electricity and other high-current applications. Owing to fundamental problems, those superconductors would never be able to carry large currents. Reluctantly, Alex Müller and I followed the advice and kept quiet for a while on that aspect, hoping that the future would prove him wrong. Indeed, the anisotropy of the layered crystal structure of the cuprates resulted in a big difference in current that could flow within the layers or perpendicularly to them. So the low critical currents measured in ceramics with randomly oriented crystallites and additional barriers for the current in the form of grain boundaries seemed to rule out any meaningful high-current applications.

In the years that followed, thin films played an important role as model systems to study anisotropy effects in the pinning of magnetic flux lines, interlayer coupling and grain-boundary effects. These key experiments had a significant impact on the processing methods of bulk superconductors, and their performance improved significantly, which finally convinced the greatest skeptics.

Today we can say that most of the applications that had been envisaged 30 years ago have been realized, at least in the form of prototypes. For transporting electricity, several test are running worldwide based on high-temperature superconducting cables that provide a reliable supply of energy to ten thousands of customers. In view of an efficient use and reliable supply of energy, superconductor technology will become the key technology of the 21st century.

 

Were there other surprises?

After the discovery of the cuprate superconductors with a maximum Tc of 135 K, the field was dominated by the research on oxides. But then, out of the blue, came the discovery of MgB2 with a lower Tc than the oxides but still attractive for magnet applications and even current transport since at first glance the manufacturing of wires appeared to be easier than for the cuprates. I feel this is only a temporary advantage. The next surprise came in form of a new class of iron-based superconductors called Pniktides, with transition temperatures up to 58 K, which could contain elements like arsenic.

Karl Alexander Müller and Johannes Georg Bednorz at the IBM Research Laboratory (Image: Archive ETH-Bibliothek).

Many of the high-Tc superconductors showed an increase of Tc under the application of hydrostatic pressure, so high-pressure experiments could be expected to make a further contribution to the understanding of the phenomenon. In that context, it is interesting that already in the late 1960s and early 1970s, predictions were made that hydrogen, when exposed to extremely high pressures (much greater than GPa) would become metallic and superconducting at temperatures on/at the order of 100 to 200 K.

Recent high-pressure experiments on H2S have indeed confirmed that hydrogen- and deuterium-containing compounds can be transformed to a very high Tc superconductor, with Tc approaching close to RT. This should have implications with respect to the mechanism of high-Tc superconductivity.

Where is the field today? Which are the main challenges that the field faces? 

Let me come back to the aspect of applications. As mentioned, many of the ideas that came up in the first years after the discovery have been realized in the form of prototypes. Only few of them, however, have so far succeeded in making the transformation from the laboratory environment to real life. For example, not many people know that at CERN, copper-oxide-based high-Tc superconductors serve as current leads to supply currents of up to 13,000 A to more than 1200 magnets. Among the power-transmission lines currently under test as part of the conventional grid, I would like to highlight the LIPA project in Long Island (USA) and the AMPACITY project in the city of Essen (GERMANY). The installation in the US has been running since 2007 and consists of three single-phase high-Tc superconductor cables of 600 m length that connect two substations in a grid serving 300,000 homes. The power transmitted by just these three cables is impressive: with ~600 MVA, it is equivalent to the power produced by a mid-sized nuclear power plant. The purpose of the German project is to study the potential and performance of a medium-voltage (10 kV) system for distributing energy at higher density in an urban network.

This installation, the world’s first of its kind, has a 1-km-long 3-phase cable with a compact concentric design that connects two transformer stations and, as a novelty, integrates a superconducting fault-current limiter. Such superconducting fault-current limiters have made the transition out of the research laboratory, and to a commercial product, with numerous installations in power plants and conventional electrical grids.

For other applications, such as compact, lightweight and energy efficient motors and generators, the pioneering spirit in industry is lacking. But this is another example where the courage to take the risk and perform stress tests under realistic conditions is needed, which will finally pave the way for an overall acceptance of superconducting machinery as a new technology. Superconducting generators have a huge potential when it comes to harvesting renewable energy, as a 36% increased generator power output is expected by upgrading existing run-of-river hydropower plants. This would lead to an energy gain of 15 GW if all of the 12,500 European hydropower plants (with 1 – 10 MW capacity) were upgraded. And in the case of wind power generation, only superconducting direct-drive generators will enable the step to systems of 10 MW or greater. Cost arguments, i.e., blaming the currently high price of superconducting wire — which is a low demand/capacity issue — should not be an excuse at this stage. Once the technology has been introduced, tested and accepted, wire prices will become compatible to those of Cu wires.

How do you see the future paths of research?

First of all, I see an urgent need in education. Just after the initial peak after the discovery of high-Tc superconductivity, almost every university introduced lectures and courses in superconductivity. Over the past years, the number of centers that still run a curriculum in physics and materials science that offers courses on superconductivity and its application has been shrinking continuously. The field needs more young scientists and engineers again who think in an “applied” way and, through creative ideas, contribute to new applications. But also work is needed on the development of new efficient and cheap methods of manufacturing wires with improved high-current densities for electrical transport and magnet applications.

The importance of the search for new superconducting materials is exemplified by the recent high-pressure work on hydrogen compounds. Each new superconducting material with its specific structure and chemistry will eventually contribute to unraveling the mechanism responsible for the phenomenon. Together with numerical simulations, computational methods that apply mathematical theorems will then probably be able to predict new superconducting materials, their crystal structures and superconducting parameters.

Dr. Bednorz and Prof. Müller in a recent colloquium on the future applications of superconductivity. 

What is your advice to new scientists that now start their careers?

What should they avoid and what should they always keep in mind in making their next steps? The beauty of science is that dreaming is allowed or I would say even encouraged. Keep in mind that even in established fields with a long tradition there may still be surprises. So keep your natural curiosity, keep dreaming, and keep your mind prepared. Whatever field of science you decide to enter, whatever you do, do it with dedication. Don’t hesitate to change if you no longer really enjoy what you are doing. When entering a new field, be curious to explore its limitations; don’t be afraid of challenging old paradigms. A newcomer with an unbiased view, especially when courageous enough to take the risk of trying unconventional ideas may make mistakes. If you learn to regard them as opportunities for learning, they can but increase your self-confidence; you will lose the fear of diving into the unknown