Oral-History:K. Alex Müller

About K. Alex Müller

Müller was born in Basel, however, raised in the Italian speaking part of Switzerland since his parents separated soon after his birth. After the early death of his mother he spent his boyhood and adolescence in the Swiss mountains in Schiers, close to the famous skiing resort of Klosters. After the Matura in 1945 he studied physics at the ETH Zürich and finished his thesis in 1960 in the group of Prof. Busch with a work on the double perovskite SrTiO3. This compound was intensively investigated by him, and he achieved major success with breakthrough discoveries in this field. The following two years he joined the Batelle Institute in Geneva working in spin resonance. Meanwhile the IBM research center in Rüschlikon was founded where he was offered a position as scientific member to explore the field of ferroelectricity where he performed brilliantly. During a two years residence at IBM in the United States he developed interest in superconductivity which he focused on in the following years. The Nobel Prize award in 1987 crowned this work but did not finalize his scientific activities which were centered on the exploration of its origin. Alongside he was, and still is, active in the field of perovskites, including manganites and ferroelectrics.

The interview was conducted during a trip to Geneva and a short stay there. While his scientific career is well documented, his emphasis in this interview was on personal events which influenced him and on activities which are less known, namely his affinity to sports. Almost all his life long he was a dedicated skier with excellent accomplishments even being in an age above 80. In addition, he has a pronounced affection to swimming which he is still practicing today. These outside of science activities are of fundamental importance to him since they helped him to get back to the roots.

About the Interview

K. Alex Müller: An interview conducted by Annette Bussmann-Holder, Max Planck Institute for Solid State Research. Conducted in Geneva, Switzerland on 24-26 August 2015.

Interview #762 for the IEEE History Center, The Institute of Electrical and Electronics Engineers Inc.

Copyright Statement

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It is recommended that this oral history be cited as follows:

K. Alex Müller, an oral history conducted in 2015 by Annette Bussmann-Holder, Max Planck Institute for Solid State Research, Geneva, Switzerland.

Interview

INTERVIEWEE: K. Alex Müller
INTERVIEWER: Annette Bussmann-Holder
DATE: 24-26 August 2015
PLACE: Geneva, Switzerland

K. Alex Müller: Milestones and Perspectives

Early Years

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My way, scientifically as well as personally, was never planned. I was born on April 21 in 1927 in the vicinity of Basel, Switzerland as the only child of my parents. Being a very young child, my parents separated and my mother went back with me to her parents’ home in the Italian speaking part of Switzerland. My mother was fluent in the Italian language and I am still speaking it fluently.

At the age of 11 my mother passed away and the responsibility for me and my future life was passed to my father. He proposed that I should attend the gymnasium at the Evangelical College in Schiers, in the eastern part of Switzerland. Only occasionally I visited my father’s luxurious home which was in a strong contrast to the unpretentious ambience of the college. His second marriage and the birth of my stepbrother were a strong challenge for me to intensify my studies. I obtained the baccalaureate (Matura) in 1946 which was by no means self-evident. Out of originally 37 pupils only a dozen passed it. The time in the Swiss mountains from 1936 to 1946 was essential for me since many deep friendships date back to these years. In addition, I became a passionate skier and practiced this until a few years ago. Each year I happily looked forward to the skiing season in the Swiss mountains and spent many relaxing and enjoyable hours on my skis. The decision to stop skiing a few years ago was very hard for me, but health and safety forced me to do so. A more detailed account of my views on sports is given in an extra chapter below.

After 1946 I started studying Physics and Mathematics at the Swiss Federal Institute of Technology (ETH) in Zürich. The courses by Wolfgang Pauli, which I attended, deeply impressed me and were a milestone in my fundamental understanding of quantum mechanics. These challenged my ambitions and helped me enormously in my further career. After receiving the diploma I had the intention to work in industry where an increasing demand for physicists was established due to the growing importance of semiconductors, magnetic elements and nuclear physics. However, I was not in a hurry, even though inspired by physics. My feeling was to have plenty of time, an impression which remained valid throughout my life and even nowadays is present.

Nevertheless, I worked for one year in the department for industrial research and returned after this experience to solid state physics in the group of Prof. G. Busch to improve inaccuracies in a conductivity and Hall measurement apparatus which I had built during my diploma work. Because of my hobby as a radio amateur, in the group of Prof. G. Busch I had the reputation of being capable in electronic circuitry , a field which at that time was much closer to my interests than solid state physics. The proposal of Dr. E. Moser to build an apparatus for the measurements of paramagnetic resonances was thus much welcomed by me since the knowledge of microwaves was requested. Together with a diploma student I demonstrated that specific manganese centers in grey tin are inaccessible by paramagnetic resonance, since manganese is not incorporated in grey tin. In this rather tenuous situation and fighting in addition with health problems I met my wife Inge.

In 1956 I married Ingeborg Marie Louise Winkler, a sister of a colleague in my group. From then scientific as well as health related problems experienced a turnaround. Her Prussian discipline was a driving force for me to finalize my thesis at the end of 1957 at the ETH in Zurich. This admirable attribute of her was and is a strong propulsion for me to live in a rather regulated manner.

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One year after our marriage our son Erich was born in 1957 followed in 1960 by our daughter Sylvia. My wife and the children with their families played and still play an essential role in my life. They accompanied me during all periods of my career and are an anchor for my philosophy of life and science.

In these years my knowledge of the paramagnetic resonance in the double oxide SrTiO3 attained a profound scientific and philosophical importance for my professional career. After my dissertation I went to the Batelle Institute in Geneva in order to investigate by means of spin resonance the radiation damages in graphite. The reason for this was a reactor accident in Windscale, England, where graphite was used as moderator material to decelerate fast neutrons. These damage partially the graphite lattice thereby spontaneously emitting distortion energy. The lattice is heating up and a chain reaction may occur which overheats the reactor which indeed had happened in Windscale. My task was to investigate how many defects are created under neutron scattering. This work was not only interesting from an applied perspective, but also scientifically which led Prof. Ernst Brun to suggest to use this work as a basis for my habilitation. This happened in 1962. Prof. Ambros Speiser, who had just built up the IBM research laboratory in Rüschlikon, became aware of this work and offered a position to me. In spite of the fact that I enjoyed science and life in Geneva and at the Batelle Institute, I decided to accept this proposal.

Before I considered the IBM offer, and gave up my position as a project leader in Geneva, I had discovered with EPR and in collaboration with Roy Rubens, that in Ni doped SrTiO3 a center is created which is either empty or occupied by two electrons. This was at least my interpretation of the data which was not at all accepted by Roy Rubens for two years. Consequently this work was published only two years later when I was already at the IBM Laboratory in Rüschlikon. Roy Rubens argumentation against my layout was built on the fact that quite generally a defect – in this case an oxygen defect – primarily traps an electron whereas the second electron is repelled due to the Coulomb repulsion. But, here it was just the other way around. This became the first known case of a so-called “negative U” center, namely a negative electronic repulsion turning into an attraction. The terminology stems from a theoretical work, published 4 years later by P. W. Anderson, who was unaware of our experimental paper. These attractive centers are formed because of the displacements of the surroundings upon the two-electron capture thus causing an effective negative interaction between them. An analogous effect takes place in cuprate superconductors where it is named “bipolaron”. But, this follows later.

IBM was at the time when I started there the world wide largest producer of data processing machines. The task of the laboratory was two-fold: understanding or uncovering the physical phenomenon, storing and processing data. Also I adopted this dichotomy in applications on the one hand and scientific cognition on the other hand. In Geneva I had already developed interest in the research of ferroelectricity which is of fundamental importance for the development of memory devices. However, being in Rüschlikon, it was indicated to me to never use this concept, since at the Thomas Watson center in New York fatigue effects have been observed in these materials. The consequences are that multiple polarization reversal cycles lead to a loss of their polarization. For this reason, the primary working materials were ferromagnetic compounds where information is obtained through the magnetic direction reversal with extremely small lattice deformations. Both, ferromagnets as well as ferroelectrics exhibit a phase transformation. Upon heating them above the phase transition temperature, reverts them into paramagnets, paraelectrics, respectively.

The theoretical understanding of these phase transformations has been provided by the Soviet physicist Lev Landau and was further elaborated in Rüschlikon. Especially, I succeeded using the Landau approach to describe the phase transition of SrTiO3 at 100K, when the oxygen octahedra start to rotate around their fourfold axis. This rotation represents the order parameter of the phase transformation, and its temperature dependence has been measured in Rüschlikon. In addition, at Bell-Telephone Laboratories the frequency of the so-called soft mode was detected by Raman scattering covering a temperature range from room temperature to the lowest accessible temperatures. The scientific community considered this as a breakthrough success, and I received for it my first distinct award at IBM. Many particles participate in such a transition and their interaction with each other and their microscopic properties are understandable within the concept of “many-particle-physics”. This perception has been introduced to me by the former head of physics and the later professor Harry Thomas. Before this time I was something like a “single-ion-man”, investigating the paramagnetic resonance of tri-, four- and five valent ions. Many particle physics established a new and important research activity for me. The corresponding measurements have been carefully carried out by Walter Berlinger. These evidenced that in the vicinity of the phase transformation deviations from mean-field theory exist.

During this critical period of time, my colleague at IBM and the later titular professor Toni Schneider hosted Prof. Amnon Aharoni from Tel Aviv, an expert in the field of critical phenomena, which cause the deviations from mean-field theories near the phase transitions. These critical phenomena, i.e. discrepancies to so-called average field theories including Landau theory, had been observed at the gas-fluid and other, e.g. magnetic, transitions already since a couple of years before. In order to describe those, Ken Wilson introduced the concept of renormalization group theory for which he was awarded with the Nobel prize in physics in 1980. I have discussed the self-similarities in the renormalization process during one semester with Prof. Armin Tellung and achieved their understanding with his aid. The critical properties of systems in the vicinity of a phase transformation is on one hand characterized by the system’s dimensionality, meaning linear in one dimension, two dimensional in planes, or three and hypothetical four dimensions, on the other hand by its symmetry class of interactions. It turned out that uniaxial pressure modifies the symmetry class of the phase transition in SrTiO3 and consequently its critical behavior. These experiments enabled us to classify the transformation as Ising type, bicritical or cubic. It was thus possible to identify a critical end point as a function of temperature and pressure. Our measurements were also the first ones evidencing a three dimensional Potts behavior whereby the system approaches in a jump like manner the transformation to change it to first order.

This work together with the ones of Heinz Rohrer and Toni Schneider contributed enormously to the scientific reputation of the small IBM Rüschlikon laboratory. Basically, this breakthrough and success which I had attained at the age of 53 years could have been the end of my scientific career to further being dedicated to management functions within physics.

The Time in Yorktown Height from 1978 to 1980

However, things evolved differently. Again the IBM management suggested to me to spend a couple of months at the IBM Research Center in Yorktown Heights (N.Y.) with the ulterior motive that I move my research interests towards new research fields. The situation of my family forced me instead to insist in a minimum of one year stay which turned out to extend over a two years period. During this time I achieved major successes within three projects carried out in collaboration with highly respected colleagues. The first one was to demonstrate the existence of the Fermi glass. This concept had been formulated by the famous physicist at Bell Lab, Phil Anderson, based on the behavior of carriers in a stochastic potential of a crystal. The second was my participation in an enormous problem arising within the IBM using electron spin resonance methods. At that time computers were equipped with single transistors deposited on isolated circuit boards which – comprising up to ten pieces – were placed on top of each other and connected to each other vertically. These boards consisted of aluminum oxide, and IBM had undertaken huge efforts in order to apply this technology in their computers. When starting the production it turned out that the connection between the individual boards was in part interrupted. Upon burning the boards they shrunk in a different manner due to the diverse orientations of the aluminum oxide grains. Here I succeeded together with Farouk Mehran, to contribute essentially to the production process of the aluminum oxides powders using the method of electron paramagnetic resonance (EPR). Most likely this is the only direct and successful application of EPR in a production process which was acknowledged by the American Ceramic Society. The third project was related to superconductivity.

In view of the success achieved within these projects I was awarded as an IBM Fellow back in Rüschlikon. This status enabled me to choose independently the direction of research which I was most interested in, namely superconductivity: the only topic of condensed matter physics which I neither had understood being 53 nor ever had worked in.

Before I moved to the research center at Yorktown Heights in fall 1978, I visited the Tel Aviv University upon invitation of Prof. Aharony, to discuss problems related to critical phenomena with him. He introduced me to his colleague Prof. Guy Deutscher who was involved in the research of superconductivity and had conducted his PhD work under the auspices of Prof. de Gennes in Paris. Prof. de Gennes was the author of a famous and well-known book on superconductivity. He was of the opinion that superconductivity could not provide new challenges and discoveries in the future. A topic which was intensively investigated in Tel Aviv, namely granular aluminum, started to attract my interest. This system consists of small aluminum particles which are embedded in an aluminum oxide. While pure aluminum undergoes a superconducting transition at 1.1K, the one of granular aluminum is more than doubled and reaches 3K. This was rather unexpected and attracted my attention, since I had the hope to observe the transition between normal and superconducting state by means of EPR, a method which had already been used to identify the traces of the conduction electrons of aluminum. Two samples were given to me, which I handed over to the very talented physicist Mel Pomeranz in Yorktown Heights, indicating my ideas for the respective experiments. The two compounds did, however, not show any EPR signal, since the EPR relaxation times are too short to observe them, a fact which I only much later being back in Rüschlikon could demonstrate. The experiments evidenced instead, that in the vicinity of the phase transitions the microwave cavities in which the samples were inserted, changed the inductivity , i.e. the frequency shifted together with a strongly modified absorption. This had never been reported before and we followed this observation with increased interest. Since Mel and myself were more or less completely ignorant regarding superconductivity, I proposed to establish a study group with the aim to understand the at that time most famous textbook on superconductivity by Prof. M. Tinkham from Harvard university. Besides of Mel and myself, Alexander Malozemov and Eleen Alexandrini joined the project. Thereby we gained sufficient insight into the physics of conventional superconductors enabling us to interpret our experimental data. We arrived at the conclusion that the transition from normal to superconducting must be a percolative process in granular systems, meaning that superconducting regions already exist above the transition temperature, expand with decreasing temperature and cover the whole sample at the transition. We summarized our results as a letter for publication in Physical Review Letters. The management, in turn, consulted another colleague for refereeing who represented the opinion that the phase transition is a consequence of phase fluctuations and consequently denied the publication of our paper. It took me estimated three weeks to obtain the approval for publication. The manuscript received excellent reports and immediate acceptance was recommended. Furthermore this paper was the origin of an invitation to the famous Harvard University to give a talk on these results there.

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Since I had adopted a substantial understanding of superconductivity in Yorktown Heights and even contributed to it myself, I announced, after returning to Zurich, an introductory lecture on this topic at the University of Zurich in spite of the fact that superconductivity was investigated in the group of Prof. Jan Olsen at the ETH.

While Mel Pomeranz at the IBM research center continued his investigations on granular aluminum superconductors, I went back to ferroelectrics using my favorite tool of EPR. In parallel I investigated by means of additional doping potassium dihydrogen phosphate, the second ferroelectric compound discovered after Seignette salt by Prof. Busch and Prof. Scherrer in 1936, and BaTiO3. The latter had attracted increased interest after its discovery by Soviet physicists and was considered to be the prototype of perovskites. Upon cooling, BaTiO3 exhibits three successive phase transitions, which have been classified as order/disorder in the US whereas W. Cochran attributed perfect mode softening to them, i.e. a displacive character. This latter description was generally accepted and the order/disorder aspects discarded. In 1985/86 I succeeded to demonstrate that the transition from orthorhombic to rhombohedral is of order/disorder character by replacing the four valued titanium in part by the isovalent manganese. This work is even today – 30 years later – considered as pioneering. Collaborations with Prof. D. Völkel of the University of Leipzig and in more recent work with him on the same samples as used in 1985 highlighted these aspects and contributed to a further understanding of the order/disorder aspect.

Workshop in Erice (1983)

During two decades my interest in ferroelectrics and my own work on them had vanished behind a curtain. The reason for this was the discovery of superconductivity in a ceramic copper oxide. In 1983 Prof. Heinz Bilz from the Max-Planck-Institute in Stuttgart invited me to participate in a “workshop” in Erice, Sicily. His and my interests focused on condensed matter physics with emphasis on ferroelectrics. In parallel to the workshop organized by him, two other workshops took place in Erice, namely on chaotic properties in many particle systems organized by Leo Kabanoff, Brown University, and on magnetic properties in condensed matter organized by Roger Elliott from the Cavendish Laboratory in Oxford. Since all three workshops offered talks in which I was interested, I listened to those for which I had a certain priority. One of the talks was given by my friend and former boss at IBM, Prof. Harry Thomas, meanwhile Ordinarius at the University of Basel. He reported on a work of his PhD student Heinz Höck, where the concept of Jahn-Teller polarons was introduced. They assumed that in a linear model the ground state of ions is degenerate. Using the famous Hamiltonian of Holstein and applying a variational method to it including carriers, they demonstrated and predicted the existence of Jahn-Teller polarons. The basic ingredients of the theory are that if the tunneling overlap between neighboring states is small, a local Jahn-Teller effect becomes effective. On the contrary, if the tunneling is substantial, the carrier hops from one lattice site to the next thereby causing a local distortion of the lattice, named Jahn-Teller polaron by them. Prof. Harry Thomas' interest in the Jahn-Teller effect originates from the time when we both were in Rüschlikon. At that time I investigated in single ions the behavior of locally degenerate states by means of EPR, the Jahn-Teller effect. Two theses at the university resulted from this work. The behavior of these ions in the excited state is also nowadays still in my mind.

After the report by Harry Thomas, I was walking across the medieval city of Erice, the former residence of the vice kings of Sicily. Next to the castle in the attached park I sat down on a bench and reflected whether there would be a system to realize such mobile Jahn-Teller polarons – eventually even in the context of superconductivity as Harry Thomas had indicated. Looking down on the ocean the idea came up that it might be possible to realize those quasiparticles in oxides. Also I thought about a person to support me. Georg Bednorz came to my mind who was employed at the IBM in Rüschlikon after finishing his thesis under the supervision of Prof. Gränicher, the later president of the Federal Institute for Reactor Research, and myself. In his PhD studies he was growing single crystals of SrTiO3, LaAlO3 and their mixed crystals according to my suggestions. Professor Gränicher proposed the method to grow the samples based on a bulb oven in which a ceramic rod was heated via lenses using high power infrared lamps. Georg Bednorz has improved this oven in Rüschlikon by installing two diametrically opposed lamps.

Work on Lanthanum-Nickel-Aluminate

Back in Rüschlikon I contacted Georg Bednorz. In 1964 two physicists from the Naval Research Lab in Washington had succeeded in inducing superconductivity in SrTiO3 by reducing it as proposed by Dr. Marvin Cohen. Instead of reducing SrTiO3, Georg Bednorz doped it with the five valued niobium in order to obtain more carriers than induced by reduction. After then Gerd Binnig observed superconductivity above 1K by a tunneling experiment. He clearly evidenced that superconductivity is not only related to a single band but to two bands. Even though this had been predicted soon after the BCS theory, this was the first experimental realization of two-band superconductivity. Superconductivity had emerged at a doping level of approximately 1019/cm3 which was sensationally low since in conventional intermetallic compounds an almost 1000 times larger concentration is needed. Therefore there was justifiable hope that upon increasing the doping of SrTiO3, higher transition temperature would be achievable. Unexpectedly, however, superconductivity vanished with increasing doping, a fact which was understood only two decades later.

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At this point Georg was really frustrated, and when I introduced the concept of Jahn-Teller polarons to him, he was ready after two hours only, to follow my ideas. My earlier EPR investigations of the three valued nickel had evidenced that this ion has a large Jahn-Teller stabilization energy. For this reason we started our project with lanthanum aluminate doped with three valued nickel. Why? It was known that lanthanum nickel aluminate is a metallic conductor since the nickel wave functions overlap strongly with those of oxygen. In order to avoid this strong overlap we arrived at the conclusion to dilute the compound by incorporating instead of three valued nickel three valued aluminum. Thereby we hoped to achieve a reduction in the band width of nickel. After two years of intense research we found out that upon cooling the conductivity vanished completely at low temperatures, i.e. a localization of carriers took place. The reason for this behavior was the existence of a stochastic potential in the mixed crystals which causes the localization. After intense discussions we decided to move from the three valued nickel to the double valued copper where the Jahn-Teller stabilization energy is of comparable order of magnitude as in nickel. Georg started studies on perovskites with copper ions and thereby came across with the work of Michel and Raveau from Caen in France. This group was engaged in catalysis and had already synthesized materials, knowing that in these compounds the oxygen ions are mobile what is essential for the catalysis. Georg started to fabricate these materials, however using a different approach than the people in Caen had established. He began with a precipitation process from an aqueous solution followed by calcination.

The Breakthrough

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When measuring the conductivity Georg first noticed a decrease in the resistivity followed by an increase with decreasing temperature. Similar observations have been encountered by us already for the mixed crystals of lanthanum aluminate and nickel aluminate. For some samples he detected at even lower temperature a clear decrease in resistivity to unmeasurably small values analogous to superconductors. However, the onset temperature was at 30K or even 35K, more than 10K higher than any other known superconductor. Our primary hope was to demonstrate that ceramic copper oxides are superconductors at all, not expecting these large values. In order to have a clear proof of superconductivity, the existence of the Meissner effect, i.e. the expulsion of a magnetic field by the compound, still had to be demonstrated. The suited susceptometer was not available in our small laboratory. A corresponding request to diverse companies yielded a minimum time of delivery of four months. The equipment was ordered and simultaneously we started preparing a publication. Early April it was finished. The choice of a journal was very delicate for two reasons: in our paper we described in detail the fabrication process of the samples which enabled any person familiar with the field to reproduce them within a few days. In case we would submit the paper to a renowned journal and as referee someone from e.g. Bell Labs would receive it, it would be tempting for him to repeat our experiments. In addition, we had to take into account that Georg was still very young and had published a number of important papers, and in case the magnetic measurements would not confirm superconductivity, it would impair his further career. For these reasons I suggested to submit the paper to Zeitschrift für Physik (Condensed Matter), edited by Springer. The today’s Prof. Eric Courtens was editor of the journal and had his office just next door to mine. I explained our experiments to him and submitted the paper to him with the request not to show it to any other person. He kept his promise with exception of a single person. He sent a copy to Prof. Thomas who pointed out to us that we should mention the thesis of Dr. Höck, which we consequently did. Furthermore I proposed to him to be coauthor of our paper since he had been the one who initiated the research on the existence of possible Jahn-Teller polarons. Harry, however, did not quite trust our work for reasons to be mentioned later and refused the coauthorship. Otherwise he would have been nominated a Nobel prize laureate together with us a year later. Of course, I invited him and his wife Waltraud to be present at the nomination procedure in Stockholm where we had a wonderful time together. For two decades we were disputing about the real reason behind the discovery.

Back to the summer of 1986, finally the susceptometer arrived in Rüschlikon. Georg detected in the same sample, in which the resistivity exhibited the drop below 35K, also a decrease in the susceptibility. This was the proof that the copper oxides are indeed superconducting. The first samples were not single phased. By means of susceptibility data, we were able to identify the phase with the superconducting properties. This was lanthanum copper oxide with partial replacement of lanthanum by barium in order to obtain defect electron conductivity. Accordingly we wrote a paper which confirmed the discovery and submitted it to the high ranked Euro Physics Letters journal. Unfortunately the editor was a well-known physicist who delayed the publication in an unfair manner until the German physicist Prof. P. Fulde intervened. Prior to this publication our guest Masaki Takashige came to us to show us an article in the biggest Japanese journal Asahi Tribun. In this article it was reported that the group around Prof. Tanaka in Tokyo had succeeded in reproducing our samples and confirmed superconductivity.

World-wide Research in High Temperature Superconductivity

For Georg and myself the confirming measurements from the Japanese group were a great delight since we had expected that the reproduction of our data would take a couple of years. The group of Prof. Tanaka, however, reacted directly, possibly related to the fact that they had discovered superconductivity in the perovskite barium-lead-bismuth-oxide at remarkable 11.2K. The next confirmation of our results came from the Bell Lab group of Prof. Batlogg, who also had investigated a related Bi perovskite compound for superconductivity. This group was exceptionally well suited to synthesize perovskite oxides. However, instead of barium, they used strontium as a dopant since strontium has a comparable ionic radius as three valent lanthanum. Barium has a larger radius and consequently causes a static lattice distortion. Batlogg and coworkers achieved a higher superconducting transition temperature than we, namely 38K. By the way, the results of the Japanese group had been presented rather successfully in the US shortly before Christmas. In the meantime spring had arrived and the meeting of the condensed matter division of the American Physical Society was ahead. Another group, confirming our data, was the one of Prof. Paul Chu from Houston, Texas. This group made a certain progress as compared to us since they used a hydrostatic pressure medium and applied this to the LaSrCuO compound. They found out that increasing pressure yields an increase in the superconducting transition temperature up to 50K and higher – an unusual behavior of a superconductor. In order to replace the external hydrostatic pressure by an internal one, they choose instead of lanthanum, yttrium which has a larger ionic radius. Prof. Chu phoned me after having obtained the pressure data and told me that it should be possible to further increase the transition temperature. This happened indeed and an unbelievably high temperature of 90K was realized. During this period of time reports from Beijing were released with even higher transition temperatures than the La compounds most likely caused by impurities in the rare earth elements. Soon it was, however, clear that the new compound has another structure as compared to the one discovered by us in Rüschlikon. A certain race in determining its structure took place, being won by Bell Lab before the IBM Lab in Almaden in California succeeded to solve it.

At the condensed matter division meeting of the American Physical Society Paul Chu proposed a special session dedicated to high temperature superconductivity, the name now used for copper oxides as introduced by Prof. Brian Maple from San Diego, California. Being invited there as invited and first speaker, I attended this session scheduled for the evening of the 27’th of March. Together with Prof. Tanaka, Prof. Chu and Prof. Batlogg we were sitting at a table in front of the audience in a huge ball room of the New York Hilton Hotel. Since this room was rapidly overcrowded, a second room had to be opened admitting for the presence of 3200 participants. This event is now known as the “Woodstock of Physics” and marks a historical date. I left the session around midnight since I was tired, but was told the next day that it continued until 3a.m. The enthusiasm was enormous. Next morning after breakfast I went along the Broadway in the direction towards the Hilton, when an unknown person suddenly greeted me with “Hallo Mister Müller”. This was a completely unexpected experience for me being recognized in the anonymous crowd of New York.

After this meeting further international reports on successes followed. While the copper oxide of Houston consisted of two CuO2 layers, in Japan a compound containing bismuth was produced with a transition temperature of 125K. Being back to Zürich in the summer of this year, Dr. Andreas Schilling, a member of the group of Prof. Ott of the ETH, managed to fabricate a sample containing mercury. This had a transition temperature of 135K at ambient pressure. Prof. Chu applied also to this compound hydrostatic pressure and increased the transition temperature 163K. It is important to mention that the single layer compound containing mercury was first discovered in Russia. When the group around Prof. Raveau explored their systems, originally designated for catalysis investigations, for superconductivity many of those were monitored as superconductors. This implies that the search for this phenomenon was essential. From all the above it is obvious that the contributions from Europe, Russia, Switzerland, and the US and Japan happened early on.

It is well conceivable that an essential interest focused on understanding the origin of the high superconducting transition temperatures in copper oxides. This is even more true since the conceptual polarons carry a magnetic moment which upon their movement through the lattice should reverse those of the two valued copper ions. The arguing centered on the fact that this should render these quasiparticles immobile and thus ineffective in superconductivity. Already before the discovery Dr. Julius Ranninger together with Dr. Alexander S. Alexandrov from Grenoble had published a paper on bipolarons, i.e., quasiparticles which consist of two polarons and are thus nonmagnetic. Independent of their work, also Prof. Jorge Hirsch from San Diego, California, had published a related work. A. S. Alexandrov, V. V. Kabanoff and Prof. N. F. Mott in Cambridge (AKM) wrote then a very famous letter published in Physical Review Letters, where they suggested the doping dependence of bipolarons, which is still valid. In parallel the groups of Batlogg and Bourne measured the isotope effect, where the typically present 16O is exchanged by 18O. In classical superconductors such an exchange causes an isotope effect on the transition temperature to lower temperatures where Tc ˜ M-? and ?=0.5. This prediction was a main ingredient of the BCS theory and has been verified in almost all classical superconductors. In contrast to the BCS theory, the above mentioned two groups did not see any isotope effect at optimum doping, thereby promoting theories based on purely electronic mechanisms where lattice effects are absent. Examples for these theories are, e.g., the RVB (resonating valence bond) idea of P. W. Anderson and the t-J model of Maurice Rice. Unfortunately the Bell Lab people ignored the work performed in the group of J. P. Franck at the University of Alberta, Edmonton, who verified pronounced isotope effects at smaller doping. Being convinced by their own results, they just did not consider this work until today, a scientifically unacceptable behavior. Muon spin rotation measurements (µSR) at the Paul Scherrer Institute (PSI) have recently demonstrated that the isotope effect considerably increases with decreasing doping to substantially exceed the BCS value and adopt values even twice as big. Very recently, Dr. Steven Weyeneth and myself were able to account for all isotope effect data, where the coefficient ? as a function of doping follows a theoretical curve which has been derived in 1994 by Vladimir Kresin in Berkeley (California) and Stuart Wolf from the Naval Research Laboratory in Washington. These authors assumed that bipolarons are directed along the crystalline c-axis which was shown to be incorrect by the very active group of Prof. Hugo Keller at the University of Zürich. They convincingly substantiated that bipolarons are located in the copper oxygen planes which had the consequence that the theory by Kresin and Wolf found little interest. When studying this theory I arrived at the conclusion that it is not only applicable to the c-axis but also valid for the planes, in quantitative agreement with experimental data. These results on their own already prove that bipolarons are the essential quasiparticles in the copper oxygen planes which induce superconductivity. This fact is very satisfying for me more 25 years after the discovery since the theoretically derived doping dependence of ? reproduces exactly the isotope coefficient data as measured by many groups. The agreement between theory and experiment is as good as my earlier work on critical phenomena, and represents a comprehension of my scientific career.

An important property of cuprates is the symmetry of the superconducting wave function which is almost isotropic in conventional superconductors.

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The above mentioned RVB and t-J theories which are based on a single-band approach, predicted a so-called d-wave symmetry, meaning that the wave function is present along the main direction but vanishes in between. Several experiments confirmed these theories being envisaged as a giant triumph. However, it was completely overlooked that only surface sensitive experiments (very short coherence length of Cooper pairs) accounted for this symmetry. On the contrary bulk sensitive experiments, like susceptibility measurements by torque magnetometry carried out by Ch. Rossel, M. Willemin and coworkers, revealed a substantial s-wave contribution. Later data with various tools confirmed this finding. These properties have been reproduced by a vibronic theory of A. Bussmann-Holder and H. Keller, which is equivalent to the bipolaron approach. This theory is based on a two-band model, where the coupling to the upper oxygen related band is the origin of high temperature superconductivity, while the copper related d-band one does not. This is altogether rather satisfactory.

Of course, world-wide diverse experimental probes have been used in exploring the properties of cuprate superconductor. To account for all of them is beyond the scope of this article. Here I want to detail results stemming from magnetic resonance which was my original working tool. For classical superconductors, the nuclear magnetic resonance and relaxation, i.e., the transfer of the nucleus absorbed microwave energy to the lattice, has played an essential role. The BCS predicted a reduction of the relaxation at the onset of superconductivity, well known as Hebel-Slichter peak. Interestingly, this was not observed in the cuprate superconductors suggesting that a substantially different mechanism must be at work here. The many results obtained in this field have all been interpreted within a single-band theory based on purely electronic mechanisms. The results on electron paramagnetic resonance – my original field of activities – were different. Here success was achieved in the interpretation of one electron spin resonance line, which was discovered at the University of Darmstadt in the group of Prof. B. Elschner by his PhD student J. Sichelschmidt. Boris Kochelaev was able to proof that the observed signal is consistent with a so-called three spin polaron where two spins are located on the copper ions and the surrounding shows a Jahn-Teller degeneracy. Based on his work the Ljubljana group of Mihailovic and Kabanov identified the intersite Jahn-Teller bipolaron. This quasiparticle consists of two Jahn-Teller polarons which are oriented antiparallel to each other with spin zero in accordance with the above mentioned proposals by Alexandrov, Kabanov and Mott (AKM).

Kabanov and Mihailovic derived their model not only from the above quoted work on electron spin resonance but also motivated by the results from structural x-ray diffraction performed in the group of Prof. Bianconi in Rome. They demonstrated that in La2-xSrxCuO4 (LSCO) not only undistorted octahedra are present but also Jahn-Teller distorted ones. Furthermore, data from Prof. Egami were taken into account based on inelastic neutron scattering, showing anomalies in the phonon mode dispersion as a function of the wave vector for specific propagation directions.

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Peculiar and specific is that the superconductor by itself does not show any response in the electron spin resonance, in spite of the fact that the +2 valued copper ion is magnetic. Many famous people like Prof. R. Orbach and Prof. P. W. Anderson have tried to unravel this miracle, however, without success. At that time I suggested to Prof. A. Shengelaya to investigate these superconductors by replacing copper by the two-valued manganese ion thereby observing well defined EPR lines. As a first result, we understood why the doped superconductors did not show any EPR response. This is due to the fact that the time between absorption of a microwave quantum and transmission from the copper ion to the lattice is too short leading to extensive line broadening. Upon cooling the samples a sharp resonance line appeared stemming from the manganese ions, which substituted in metallic aggregates. This happened already at very small doping of only 1 - 6% where the compound is not yet superconducting. From the intensity increase of this line upon cooling we were able to extract the formation energy of the bipolaron caused by two Jahn-Teller polarons, namely 500K. This confirmed on the one hand the AKM phase diagram based on a doping dependent association energy, on the other hand corresponded within error limits to the ground state energy of these Jahn-Teller bipolarons as derived from first principles calculations. Two electron spin resonance experiments thus contributed to the understanding of superconductivity in cuprates. Furthermore, the EPR experiment accounted for the fact that already at small doping bipolarons agglomerate in metallic aggregates, corresponding to a dynamically inhomogeneous system. Consequently many theories including purely electronic ones are discarded. At small doping metallic regions or stripes are embedded in an antiferromagnetic insulating matrix supported by susceptibility measurements of the group of D. Johnston from Iowa state university.

My final success achieved at the age of well above 80 years represents the conclusions on the properties of the high temperature superconductors, discovered by Georg Bednorz and myself.

Sport and its Importance to Me

As already mentioned in the beginning, when starting in Schiers as a pupil, I was rather health wise unstable. However, two types of sport activities considerably helped me in gaining strength and health. In summer I became a devoted swimmer, whereas in winter I became a passionate skier. At the age of 12 I was unable to swim in contrast to most of my classmates. Obviously I had been sheltered too much during my time in Lugano. In the fall of 1939 I returned from a trip with my father to the Mediterranean Sea where I failed to apprehend swimming, back to Flims, where we stayed at the still existing hotel Segnes. My father was frequently on business travels in the area of the lowlands whereas I lived in a room of the villa vis a vis to the hotel, reading Indian sagas. During day time I went to the swimming bath of the Cauma lake to see the bath attendant Casparis, who was teacher at the school of Flims during the year . After a couple of lessons I was able to swim one length of the inner part of the basin. When the Second World War began and the general mobilization was announced in Switzerland, I watched my swimming teacher joining the Generally staff. Since my father as a mountain artillerist was also called to arms, he took me back to the institution in Schiers despite the fact that the summer vacations were still ongoing. In the following summer 1940 my grandmother Müller rented the Villa Caumasee opposite to the homonymous pension for the whole family. Each sunny day I went for swimming in the Cauma lake. First I managed to swim from the swimming bath to the nearby float, from there to a little rock and finally to the big island. In that summer I was 36 times at the lake and at the end I managed to swim from the peninsula, surround the island and back to the swimming bath corresponding to approximately 300 to 350 meters. Frequently I was taking a sun bath, watching the people or reading the books of Karl May which my father had given to me. Never ever anybody accompanied to the swimming bath, and I never mentioned it to either my grandmother or my aunt with her two children and the cook. During this time my father attended the military service and visited us once or twice. He was rather disinterested in my swimming experiences and swam himself only where he could still touch the ground. At the end of these vacations I had become a tanned healthy 13 years old boy.

Since then I was swimming each summer when the weather admitted for it, and yet nowadays I do so even though I am using crutches. This summer I swam in the Laaxer lake along its full length of 250 meter and back. When we bought the apartment in Salums/Falera in 1984, my wife and I drove to Flims, parked the car in the forest close to the hotel Adula, hiked to the cable car and continued at its lower end towards the area of the Cauma lake to spend all the day long there. Both of us were swimming from the peninsula, surrounding the island and back. Inge was never much interested in sports activities. However, she always spent the summer in Stolp (now belonging to Poland) with her grandparents, who leased a huge manor in Pommern close to the Baltic Sea. There she became a swimmer. During two summers we enjoyed the concerts initiated by Justus Franz while staying in Preetz/Schleswig-Holstein. On one occasion we drove in the direction of Rostock and took a bath in the Baltic Sea. At that time Inge had already reached the age of 80. This became an enjoyable anniversary. Two years ago I swam the same distance in the Cauma lake as I had done 73 years ago, of course without company. Typically my style was breast stroke followed later on by backstroke. For many years I was eager to swim the crawl, also with the help of swim masters, however, I never managed to do so. The reason was my incorrect leg movement. Being 75 I was swimming my usual almost daily round in the Hedinger-Weiher, when I tried it again and – I was successful. You might imagine my delight that I had succeeded with this sport close to old age. This happened only 13 years ago, and also today I am mostly performing back crawling since it is an even movement and avoids water to splash into your face.

I learned skiing early on. When I was still staying with my mother in Lugano, I spent part of my school vacations in a children’s institution in Celerina in the Engadin, in summer as well as in winter. In the winter I started in the lowest class of the skiing school. After the death of my mother and my move to the villa Sumatra in Chur I urged for skiing. In 1938 my aunt and godmother Margrit Piaggio-Müller took me with her to Arosa for a couple of days after Christmas. In the following winter I accompanied my father for a few days to Lenzerheide in the chalet God Lai. There I attended the skiing lessons of Willi Paterlini, a son of the architect with the same name. I graduated effectually the first examination of the Swiss skiing club with a silver medal. In later years in Schiers I was guest of the reverend Middendorp and his wife in their beautiful chalet in Klosters. The reverend was a member of the administrative council of the institution, had been reverend before in Klosters and was still pastor of the Dutch tuberculosis hospital in Davos. He was a real chess player, and I had several opportunities to challenge him. His wife, actually the second since the first had died from tuberculosis, managed the house as a pension for youngsters who visited Klosters during the vacation time. In addition, also elder people stayed there to recover from their treatment at the hospital. Due to the unavailability of heating material during the Second World War, the winter vacations in Schiers were extended, which allowed me to take part in skiing lessons in Klosters. I managed to reach the uppermost grade in the 6’th class, the so-called racing class, where I received the gold medal, wearing this full of proud. In order to obtain this medal, several examinations had to be passed: one route in a racing manner, a powder slope using the old fashioned telemark turn, in classical as well as the Kristiana assembly, the parallel sweep, and then down swinging. For the latter one a special binding with diagonal drills around the heel of the boots is needed in order to keep the frame on the skis. For Christmas my most favorite gift was a subscription eligible for 8 days for 48.- SFr. By considering that the money at that time was almost 10 times worth of nowadays, the amount at that time corresponds approximately to the one of today. The subscription comprised the access to Rähtischen and the new Parsenn route. During sunny days I used it either starting from Klosters or from Schiers, however, rarely from Chur.

On such a day I was skiing in the morning and afternoon along the standard ridgeway track from the Weissfluhjoch to Davos, which descends steeply down from the village mountain. In the early evening I crested the “Bretterwand” above the Weissfluhjoch where a steep rock slope requires some keen sweeps to follow further the trail in the direction of the crossing way, where the trail branches in either the direction to Klosters or straight ahead towards Küblis. This track has a length of 12 km and leads through the village of Conters. On this track I used to stop for a break during sunny days and observed the mountains of the Räthikon across the Prättigauer-Tal heading towards the Montafon in Austria. The sunset illuminated the scarp face of this druse aspic of the mountains with an orange-yellow light. This landscape contrasted against the blue colored sky and the darkening valley of Prättikon was a veritably memorable and sublime impression which even today releases gratefulness to me and is a part of me. Frequently I was on my own, an attitude which I adapted also later on. The tension, which I experienced as manager and scientist at the IBM, was released when I made my own way in the mountains far apart from and with sufficient distance to the evolutions down in the valleys. It was important for me to adopt a perspective to differentiate between irrelevant and relevant incidents. In addition, I gained fierce to continue also in difficult situations.

During my grammar school time I was occasionally skiing with boys of the same age, who also spent their vacation in Klosters. I remember one of them, named Wehrli, the sun of a silk fabricant from Zürich. He was accompanied by his elder sister, well dressed and built. At a first glance I categorized her as a fashionista, however, I had to revisit my first impression when watching her skiing. She was handling this very well using the latest techniques. I have no idea what has happened to both of them and how they are doing now. On a warm spring day after Easter 1944 it was almost fateful that I had a companion. It was Thomas Egli, the sun of the owner of a health food store in Zürich. We had climbed up to the formerly mentioned “Bretterwand” above the Weissfluhjoch, to continue in the direction north close to the crest . We reached a perfect powder snow slope down to the Meierhofer Tälchen towards Davos-Wolfgang (nowadays accessible by lifts). I was the first to ski downhill thereby overlooking that it had been raining even in the highest areas only a few days ago. The slope was completely icy, and I was hardly able to stay in my track. After a left sweep with the weight on the right ski directed to the valley, this got in touch with an icy ball, the ski twisted under the left one, and I heard the bang. As it turned out later from the x-ray photograph, my left tibia had a complicated spinning fracture. I tumbled and remained lying on the right side in the middle of the frozen track. It was so late that the last track control had already passed. The only option was that Tommy went down to Wolfgang on his own, as safe as possible, to organize help and support. Meanwhile I was lying lonely on the snow without any warming jacket, since the day had started warm. I began to freeze and then to shiver since the pain made me almost immovable. Then I calmed down and a warm feeling overtook me which made me sleepy. With hindsight I am sure that this was the beginning of perishing by cold. Now my own experience tells me that freezing might be a friendly death. Therefore I well understand the Japanese practice of certain regions where the sons carry their aged fathers and mothers to an elevated frosty region where they float smoothly and without pain to death.

After an hour Tommy Egli was back accompanied by the Parsenn patroller Turner. Since no more courses were running, the Parsenn ropeway had organized an extra tour to take them to the saddle. Turner first dug a step into the icy slope in order to stabilize the Canadian saving sledge. When trying to remove my skis from the boots, it turned out that these were frozen to the icy binding. The left leg boot could be resolved with a couple of beats. The same procedure was not manageable for the broken leg which hurt too much. Turner picked an ampoule with morphine from his backpack which he injected to me, releasing the pain after a short while, and the boot cold be unstrapped from the ski. After placing me on the Canadian he carefully drove downhill towards Wolfgang. In the middle of this dangerous tour he stopped and turned the sledge to the hill to draw my attention to a pack of chamois. It is rare to make such an observation in this special situation. After the train transport from Wolfgang to Klosters I was delivered to the well-known medicine Dr. Egger. Still lying on the Canadian, the boots were taken off, and the one of the broken leg was cut apart. The doctor showed up and grumbled severely with me. I had fastened the bootlaces too tight in order to stabilize my feet. This caused a considerable danger for the blood circulation to stop in the cold and in view of the 2 hours duration to get to the doctor. There was a considerable risk of frostbites for my legs. The x-ray photograph revealed the spinning fracture which was plastered with a notch upwards in order to allow the plaster to expand with the onset of the swelling. A week later Dr. Egger arrived in the reverend Middendorp’s house where I stayed, equipped with a portable x-ray meter. He partially removed the plaster and applied a new one in order to adapt the curvature of the broken leg to the one of the healthy one. When I had to report to the military service a year later, the military medical could hardly recognize the fracture anymore. Being in the full growth period, I had suffered from a so-called “green” fracture.

During my schooldays, I took advantage of the school’s free afternoons, Wednesday and Sunday, to improve my skiing style. On Saturday mornings, 5 hours at school were mandatory. Across the river Lanquart was a steep meadow at the north rim of the Lanquart mountain, the Rosenberg. This was well suited to exercise slalom races. Flags were already used whereas bars were unknown. Especially the contra shoulder throw, introduced by the famous Rudolf Rominger, world champion and member of the Guarda of St. Moritz, could be refined by me. After the war the mid shoulder throw, as introduced by the French champions, became fashionable. With the use of the shorter carving skis the former is back now, however more subtle. In the south of Schiers behind the village Maria and continuing further to the so-called A-start to the slope for downhill skiing, requires to climb upwards for at least one hour using hides. At both locations the institution championships took place around Easter, at that time being still snow rich seasons. When attending the Matura class, I succeeded in both, down-hill and slalom skiing, to be one of the first and thus became the alpine school champion. At that time, giant slalom and super G were unknown. From the above it is obvious that the Prättigau gave distinction to my devotion for skiing. During weekends, when the chalet in Lenzerheide was unoccupied, I showed up there as a guest. After the installation of the first rope drawn Funibahn from Val Sports to the Alp Tschantieni, more and more ski lifts were established, the first to the Pitz Skalottas. On a Sunday evening I stayed for dinner, thereby missing the last post van tour to Chur. By the way, at that time the post vans were equipped with wood carburetor since the gas was scarce. For this reason I had to use my skis and moved in a skating manner on the hard pressed Kanton street to Valbella, climbed the pass and followed the street to Chur with the full distance being 17 km The rare event of cars on the street was easily recognizable by their spotlights. From Chur I took the train to Schiers to attend the school on Monday morning.

During the first semester at the ETH, skiing became a rare event. Being in Zürich it was rather cumbersome to reach the skiing areas. I always – with a single exception – spent the short time of Christmas vacation of the ETH with Mrs. Middendorp in Klosters. Her husband had already passed away. In contrast, the long semester breaks in March and April while studying were fully occupied by military services. During the first year the latter took place in the sergeant’s school including repetition courses. The following year was devoted to special courses where officer cadets were selected, again in combination with repetition courses and later officer classes. Upon attaining the rank of a first lieutenant, my military activities were reduced, thus leaving me more time for skiing. In particular, I participated in the academic skiing courses and excursions and became acquainted with the regions around Stoos (above Schwyz) and Flims. After the diploma and having purchased a light blue VW beetle, I spent the weekends exploring further winter sport areas as, e.g., Alt-St. Johann and Wildhaus in the Toggenburg region. On the occasion of my marriage, my mother-in-law, Dora Winkler, donated a couple of days stay in Mürren to us which I memorize with great pleasure. When the railroad to the Schilthorn was finalized, together with my brother-in-law and his son we tackled the difficult downhill slope to Mürren.

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As already mentioned in the second chapter, after my dissertation I adopted a position as scientific member at the Batelle Institute in Carouge near Geneva. Even though the importance, the charm and the cosmopolitanism of this city are well appreciated, these are not the issue here. For a skier the area of Geneva provides enormous prospects. For instance, after Sunday’s lunch the nearby Faucille-pass offered excellent skiing opportunities, whereas the well-known skiing places in the French Savoyen are located a little further apart. The closest one is La Clusaz which was easily manageable as a day tour. Later on, when we were already back to the Zürich area, I had a couple of scientific activities in Grenoble. On these occasions I discovered the Chateau Beau Lieu located above the city, with a panoramic view of the Alps and Grenoble. During the Second World War it used to be the quarters of the SS of Savoien. Descending from the Chateau one arrives at the nearby Chamrousse or Les Deux Alpes. The latter place is an artificially constructed skiing village opposite to the Mèche massive with mechanical skiing constructions reaching far above 3000m. Skiing there remains a truly memorable event. Starting from the same Chateau I also went to Val D’Isere. Also there the racing tracks are excellent. Later on I arrived together with my son at the place named Les Trois Vallées. These are three stations in the same region, however located at different altitudes, and connected with each other by mechanical constructions. Their concept is very modern and favored by Parisiens. The terrain is broad and well developed with the upper part enabling powder snow skiing whereas the lower part offers spring snow skiing in the afternoons.

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Back to Zürich, we spent the first Christmas vacation on the Rigi ob Art Goldau with the best slope of the Dossen, a place which I had discovered already during my winter repetition courses at the military. My family and myself spent the following six spring holidays in Andermatt in the hotel Schweizerhof owned by Mr. Escher, upon suggestion of my boss at the IBM, Harry Thomas. In the beginning we climbed the Nätschen with the RhB, from which Inge and the children used the sledge along the street to get back down to Andermatt, while I took the local lift to the Gütsch. At the Gütsch a huge artillery fortress has been constructed during the Second World War, one of the largest in the center of the Swiss alps reduits. Starting from there a rather smooth slope down to Andermatt can be taken. Next to the Schweizerhof was a little greengrocery with one of the shop assistants, named Maria, being simultaneously a skiing instructor. With her rather rough Urner attitude she guided the children skiing class such that the kids started crying and left the classes heading back to their lodgings. Soon I discovered the newly constructed Gemsstockbahn which connects to the peak of the homonymous mountain of more than 3000m height. From there three slopes could be chosen to ski downhill: the sun slope, besides of the first part rather smooth and sunny to warm up in the morning,; the slope directly underneath the cable railway, the glacier slope, very steep and narrow, which requires an excellent control of the skis; a traversal to the right into a formidable hardly used giant slalom slope. Nowadays, with the vanishing of the snow, the latter is not accessible via the traversal. Starting from the Gemsstock, it is also possible to reach the sun slope and continue to the left into the so-called rock valley. This was one of the favorite racing tracks of my IBM colleague Keith Blazey and his girl friend Christina Anselmi, both being brilliant deep snow skiers. Frequently I followed them together with my son. A number of diversified powder snow tracks exist there as well which finally end at the canton street between Hospental and Andermatt. Later, when we already had acquired the apartment in Salums/Laax, I drove on a spring day in less than an hour from Hedingen to Göschenen, following the highway to reach Andermatt. Here I enjoyed very much skiing downhill the trail to the Gemsstock.

When reading the above one might ask, whether I also practiced sports while staying overseas. Of course I did! In the seventieth the theory group around Dr. Alan Bishop in Los Alamos (now director of the whole lab) was highly interested in our results on phase transitions. In order to collaborate with this group Toni Schneider and myself stayed in Los Alamos in a local motel. From there we used to drive to a Swiss founded skiing center in Taos. The slopes were partially quite demanding. On a later occasion I drove with my rental car to the small village Red River, a very cozy place with few ski lifts far away from hectic, crowd and throng. Instead, it was a pleasant place to taste the American food and good Californian wine. At this time also important scientific connections were established with the IBM laboratory in San Jose/California. Toni and I figured out that it would be more beneficial to stay at a rate of 36.-$ in a motel close to Alta/Snowbird instead of residing in the vicinity of New York for more than 100.-$ per night. This enabled us to spend the weekends skiing in perfect powder snow. We arrived at this beautiful place by plane from the east to the west coast with one change at Salt Lake City to take a rental car. The skiing equipment was at that time still transported by the airlines without additional charge. Later I worked for two years in the large T. G. Watson Research center near White Plains, NY and remained there also during the winter season. In the first winter I was skiing in the northern part of the state of NY. However, the snow was mostly icy, whereas the wintry New York offered many attractions, especially during Christmas times when stores were gorgeously decorated, the Central Park covered by snow and the streets lovely illuminated.

During the second winter, being scientifically well established at the Watson center, I allowed myself a two weeks break in the Rocky Mountains. Taking the plane to Denver and driving with a rental car through the Eisenhower tunnel, I found a lodging in the famous Squaw Valley. The weather forecast was very convenient, namely snow during the night and blue sky during day time. At high altitude the flaky snow rested on a hard ground enabling easy swinging in untouched white snow – really formidable. The only precaution to take into account, was to protect the face from the intense sunshine. The village was structured rather analogous to Alp villages, but quite glamorous. Afterwards I moved to friends to Steamboat, rather similar to Red River, equipped with good mechanical constructions, however, smaller, cozy, content and without ambitions. The people there enjoyed their life around the ski lifts and the get-together during meals. This I had met in Europe and especially in Switzerland only once in the sixties on the Stoos ob Schwyz, when the ropeway was still the small old one and aerial passenger lines not yet installed. We went up there together with our children. At the mountain station one had to drag the skis to the beginning of the lift. From above the trails were welcoming and the view on the Vierwaldstätter lake perfect and unique. In the evening we came together in an appealing tavern for the Alphubel. During day time Inge walked to the little church, enjoyed the sunshine and the landscape, and was reading a good book while resting.

After returning in 1980 from White Plains to Hedingen, we left for spring vacations to Pontresina in the Engadin instead of Andermatt. In view of his age, Mr. Escher in Andermatt had retired. We resided in the Sporthotel from where we could take a cross-country ski run to Morteratsch. Another option was to move to the Val Rosegg to a restaurant, take a break there and return to Pontresina using a loop below the massif and the glacier of the Rosegg. In advanced age, Inge and I rented a sleigh to enjoy once again the beautiful Val Rosegg. From Pontresina we also took the car to reach the station of Morteratsch, where Inge spent the day in the sunshine in the local hotel and reading a book. I reached the Berninapass with the RhB to continue from there and depending on the snow conditions, using the overhead railway to either first to the Lagalp, a famous place for ski racing, or alternatively the Diavolezza with its famous outlook on the Piz Palü, Bernina and Morteratsch. Being a young man, my father was a well experienced mountaineer who climbed these three mountains a couple of times. The first of them can be ascended via the well visible Bianco Grat, being roped up and equipped with climbing spurs. I have never been there. From the Diavolezza a very steep and terrific downhill slope to Isola Parsa leads to the glacier of Morteratsch. Any slipping was dangerous and followed by a nonstop sliding down the long slope up to its end. From there it was possible to arrive at the place where Inge was waiting, using the glacier route to Morteratsch. Having a comfortable Zvieri (small snack), we drove back by car to the hotel. This trail is today no more in use. The crevasses are too deep and the glacier has vanished by 2 km due to the lack of snow.

For the alpine skier, the Engadin is something very special. After two winters in Pontresina we resided on several occasions in the hotel Kurhaus in St. Moritz-Bad, next to the cross country center. From there the ropeway takes you to the world-famous Corviglia. This ropeway from St. Moritz was apparently the first of its kind. The slopes down to St. Moritz are broad and easily manageable. From the mountaintop another ropeway takes you to the Piz Nair. The deep snow downhill is mostly closed, and I never had an opportunity to ski it . However, the downhill to the behind located little valley was pleasant. Furthermore, there is a lift towards the Corviglia below which a point of intersections of mechanical transport towards the ground is located. The most efficient one out of those is the one to Trais Fluors with elegant hillsides across the Val Saluver when staying on the track. The well-known playboy Gunter Sachs and his group had left this piste and had been buried by a snow slide causing several dead people. His wealth admitted him to employ a number of hotshot solicitors to escape the Swiss prosecution. Later on and on several occasions during spring time we stayed in the hotel Margnia in Sils Baselga. The main building of the hotel has historical roots, heavy walls and a famous kitchen. From the neighboring village, Sils Maria, a cable car takes you to the hillside below the Corvatsch with a couple of ski lifts. The downhill trails are unpretentious and even traversable with bad view and flimsy snow fall.

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My paean of praise for the Engadin is not yet used up. A real event is the area of the Corvatsch. The cable railway there consists of two sections and has been financed by the Greece shipping company owner Onassis, the subsequent husband of the widow Jacqueline Kennedy. Using this it is possible to arrive at the top of the mountain at 3400 m. The panorama there extends from the Grossglockner in Austria to the Italian Alps. Two options to ski down are given: parallel to the Engadin down the glacier, first being soft and broad but then becoming steep and even steeper. If this was successful, one arrives at the Surleihütte for lunch, e.g. The second trail leads via an exposed traverse to a dangerous inclination towards south. The last time that I was up there, I had already reached the age of almost 80 and went weak at the knees. This forced me to ski down performing schooling telemark turns. After the traverse, easy going curves succeed to finally end up at the Surlei. From this welcoming lodge one attains the middle station of the Corwatsch train and using the connecting lift to arrive at the Hanensee, sitting above St. Moritz. This is also in summer a worthwhile destination. In the afternoon real connoisseurs of the region gathered at the lodge for a happy get together. Afterwards, being back to the skis, one ended directly at the hotel Kurhaus by following the trail through the forest and the bushes. This is a very particular way to get back to the accommodation without walking or driving but just by using skis. Undressing the ski clothing and taking a shower is followed by a nice nap before dinner. I remember well an event happening at the Surleihütte: together with the colleague at the IBM, Dr. Frei owning a house near Samaden, we were skiing down through the deep snow without flags to the restaurant in Val Rosegg. The colleague was accompanied by his son who was not very well experienced in skiing. He tumbled and looked rather gloomy for a while, but there was no way back and we finally managed to arrive safely at the hotel.

This happened when we had just returned from the USA back to Hedingen. When we bought the apartment in Salums close to Laax, two reasons motivated us. On the one hand it was possible to easily reach the white arena, a perfect skiing region, on the other hand during summer the Cauma lake, a treasure of the Alps, situated in the forest, was ideal for swimming. There I had learned how to swim. To come to Salums from Hedingen by car took, in addition, only half the time as compared to the Engadin.

In Salums I was skiing on various trails with my three grandchildren. First I had to wait for them at the downhills, later they had to wait for me, since I became more cautious in order not to tumble what rarely happened for entire days. In case it occurred indeed, I had to slip off my skis to get up again. Thus, being 80, I approached the moment when I decided to stop skiing at all because my muscular strength was insufficient for precise skiing sweeps. Nevertheless, skiing remains with me even nowadays. My best dreams are those where I am skiing downhill in good powder snow. Whenever I have this dream, I am convinced that I am totally ok with respect to my physical conditions, my attitude to life and my knowledge. This kind of dream is rare. In contrast, the terrain is truncated, like on a glacier, and precise sweeps are needed not to fall into a crevasse, or the terrain is stony and not fully covered by snow. Then I have to carefully avoid the snow empty regions in order to prevent damages to the skis. An alternative scenario, which is typically occurring during spring, is a spot like snow distribution where jumping over the snow free section is required as I used to do as a youngster.

Altogether all my life long I had the privilege to perform skiing and to exercise it in diverse first-class skiing areas in my home country as well as in Europe and abroad and now to even dream of it.