K. Alex Müller Nobel Prize in Physics 1987

is convinced that he at last has a water- no one took him seriously. “Exactly tight explanation for the phenomenon that motivated me. I wanted to swim that he and J. Georg Bednorz discovered against the current.” 28 years ago: High-temperature super- He says that he owes his persistence conductivity in copper oxides. This and his desire to think outside the box should bring a decades-long dispute to his childhood, which was not easy, to a happy end, at least from Müller’s as Müller explains. The son of a sales- perspective. With his explanation, how- man and grandson of a chocolate man- ever, Müller has launched a new debate ufacturer, Karl Alex spent part of his on the distribution of matter in the uni- childhood in Lugano. After the early verse. But more of that later. death of his mother, when he was just Erice, Sicily, summer 1983: K. Alex eleven, he went to boarding school in Müller is sitting on a bench in the cas- Schiers. Holidays were spent with his Nobel Prize in Physics 1987 “for the tle grounds and enjoying the view. As pioneering discovery of super- he gazes into the distance, his mind K. Alex Müller was 56 when conductivity in ceramic materials” buzzes with ideas. He had just listened he decided to take on a new to a lecture by Harry Thomas which * 20 April 1927 in Basel challenge – researching dealt with the possible existence of superconductors. 1962–1970 Privatdozent Jahn-Teller polarons – “quasi-parti- 1970–1987 Adjunct Professor cles” that occur when electrons move 1987–1994 Professor of Solid-State Physics through a crystal lattice. Thomas sus- grandmother at the Villa Sumatra in at the University of Zurich pected that these polarons could result Chur, where he could forget the auster- in superconductivity. ity of boarding-school life, again eat his “As I sat there, gazing at the sea, the fill, enjoy the bourgeois atmosphere, idea came to me that such polarons and sleep on mattresses of the finest might occur in oxides,” K. Alex Müller horsehair, as he writes in his memoirs. recalls. It seemed far-fetched, as oxides From 1946 to 1952, K. Alex Müller are ceramic materials with only very studied physics at ETH Zurich, where Müller’s poor conductivity at normal tempera- he attended courses taught by Wolf- tures. But they were also very familiar gang Pauli and Paul Scherrer. Pauli, for Submarine to Müller; he had worked on them all all his methodological precision, never Zollikon, December 2014: K. Alex Mül- his life as a researcher, and had pub- lost a feeling for the unpredictability ler is a happy man. The 87-year-old lished foundational articles on them. of nature and scientific processes – an physicist sits in front of his laptop and Although he had never worked in the attitude that Müller internalized: “De- says: “I believe we’ve understood it.” field of superconductivity, Müller, at cisive events in science often occur en- Understanding something is already the time 56 years old, decided to take tirely unexpectedly.” Like Pauli, Müller special for a physicist. In this case, on an entirely new challenge. showed an early interest in psychoanal- however, the thing understood con- Müller had already voiced the idea ysis, particularly in the interpretation cerns high-temperature superconduc- that, under certain conditions, oxides of dreams. “It was always dreams that tivity, Müller’s magnum opus. Müller might become superconductive. But gave me confidence in myself and in

www.nobelpreis.uzh.ch/en_mueller.html K. Alex Müller – Nobel Prize in Physics 1987 1/4 the path I had taken,” he says, looking opments at IBM that caused Müller enjoyed the privilege of choosing his back. In 1958, Müller earned his doctor- to devote more time to research. This work as he deemed appropriate. ate at ETH Zurich and began work as came about as follows: In the 1970s, Rüschlikon, 27 January 1986: Georg a research associate at the Battelle Me- Müller was the head of the Physics De- Bednorz has just “brewed” lantha- morial Institute in Geneva. Müller has partment in Rüschlikon. At that time, num-barium-copper oxide. This, after fond memories of his time in Geneva Heinrich Rohrer and Gerd Binnig were three years of hard work in the lab- – due to the charm of the city as well developing the scanning tunneling oratory, 80 synthesized compounds, as to the birth of his daughter, Silvia. microscope that would earn them the and many set-backs, is the big break- His son, Eric had already been born in Nobel Prize in 1986. The head of re- through: A compound that will take Zurich. Family was, and remains, enor- search at IBM was so impressed by this superconductor research in entirely mously important to K. Alex Müller. He invention that he decided to focus all new directions. The critical temper- met his wife, Ingeborg Marie Louise physics research in Rüschlikon on the ature at which this copper oxide be- Winkler – his mentor, companion, and further development of this process. comes superconductive is an aston- a substantial influence on his work – K. Alex Müller opposed this decision, ishingly high minus 238 degrees. The through her brother and Müller’s fel- as he considered other projects to be findings are nothing short of a sensa- low student, Ulrich Winkler. Ingeborg equally important, and consequently tion, and the publication of the discov- trained as a singer and performed as ery unleashes a wave of enthusiasm. a soprano soloist in church concerts. Soon laboratories around the world “It was always dreams that The Müllers were regular visitors to begin to apply this new knowledge, gave me confidence in myself the Zurich Opera. with copper oxides at even higher crit- and in the path I had taken.” In 1963 Müller and his family re- ical temperatures soon being found. K. Alex Müller turned to German-speaking Switzer- Just a year later, Müller and Bednorz land after receiving a very attractive were awarded the Nobel Prize in Phys- offer: A position at IBM’s new research resigned his position as head of de- ics. However, a veritable “religious laboratory in Rüschlikon, with the partment. This freed up time for his war” still rages in physics over the the- possibility of teaching at the Univer- own research: “It was just as well; to oretical explanation behind their dis- sity of Zurich. While still in Geneva, me, research was always the most im- covery. Many physicists, particularly Müller had lectured at the University portant thing.” Looking back, it was scientists in the USA, take the view that of Zurich; in 1970 he became an ad- undoubtedly the right decision, as it the difference to conventional super- junct professor and in 1987, just before gave K. Alex Müller the time and the conductors is so great that an entirely receiving the Nobel Prize, he was ap- leisure to write physics history. new electronic theory is required. In pointed full professor. After his return He didn’t, however, make his contrast, K. Alex Müller and his succes- from Geneva, he lived first in Affoltern groundbreaking discovery alone but in sor in superconductor research at the am Albis; later, the family moved to a collaboration with J. Georg Bednorz. At University of Zurich, Hugo Keller, have house of their own in Hedingen, where that time, Bednorz, previously Müller’s demonstrated that, as with conven- Müller lived until he moved to the Ter- doctoral student, was also working tional superconductors, the interaction tianum in Zollikon; he was declared an at the IBM laboratory in Rüschlikon. of the electrons with the oscillations honorary citizen of Hedingen in 1988. ­After returning from Erice, Müller took of the crystal lattice is responsible for His double mandate at the Univer- Bednorz into his confidence and sug- high-temperature superconductivity. sity of Zurich and with IBM gave K. gested that they tackle the supercon- Today, K. Alex Müller is convinced that Alex Müller welcome room to maneu- ductor project together. Bednorz, then he has supplied definitive proof – albeit ver: “When things were not going so 33, agreed. They began their work con- proof with a surprising consequence. well at IBM, I spent more time at the fidentially, as a so-called “submarine As is the case with metallic supercon- University, and vice versa.” It was in- project.” Müller was able to research ductors, the so-called Cooper pairs – deed his dissatisfaction with devel- independently; as an IBM Fellow, he in this case bipolarons – enable the

www.nobelpreis.uzh.ch/en_mueller.html K. Alex Müller – Nobel Prize in Physics 1987 2/4 current to flow without resistance. In Proven in Zurich: num-barium-copper oxide, becomes super- oxides, however, the bipolorans are not Superconductors – conductive at minus 243 degrees. While no distributed evenly. “The areas that are Oxides Beat Metals great difference in temperature, this repre- superconductive change dynamically,” sented a huge scientific advance because says Müller. “There are some with a When, in 1983, K. Alex Müller and J. Georg the new material immediately opened up big charge, and some with no charge.” Bednorz began their search for a high-tem- new possibilities. As became quickly clear, On the back of this discovery, perature superconductor in ceramic com- the critical temperature of oxide compounds Müller has taken a bold step from pounds, superconductor research had ar- is significantly higher than in metals. Today, copper oxides to the cosmos: “When rived at a dead end. In metallic compounds, the highest critical temperature for copper you look into the night sky, you see which had traditionally been investigated oxides is minus 110 degrees. clusters of stars, areas that are light, for superconductivity, scientists were unable A high critical temperature has the great to significantly increase what is known as advantage that superconductivity is achieved the critical temperature at which a material by cooling with liquid nitrogen, making tech- Contention still rages in physics becomes superconductive. At the time, the nical applications much simpler and cheaper. today over the theoretical highest critical temperature of a metallic It is used today in power stations, transform- explanation behind Müller’s compound was minus 255 degrees Celsius. ers, medical technology, power transmission, discovery. That metals could be superconductive and microelectronics. (TG) had already been discovered by the Dutch and areas that are dark. The universe physicist Heike Kammerlingh Onnes in 1911, is not homogeneous.” In his General when he cooled mercury to minus 268.5 Theory of Relativity, however, Einstein degrees Celsius and observed that electric postulated that matter in the cosmos resistance disappeared. Further metallic is indeed homogeneous. “If he were ­superconductors were subsequently found, right” maintains Müller, “the universe and in 1933, German physicists Walther should be evenly illuminated. This is Meissner and Robert Ochsenfeld discovered not the case.” For, like the charge in the eponymous Meissner-Ochsenfeld effect, the superconductive cuprates, matter which demonstrates how a superconductor in the universe is not evenly distrib- entirely “expels” an external magnetic field uted. “Accordingly, we must rethink from its bulk. This makes a superconductor the Theory of Relativity,” Müller con- not only an ideal conduit for electricity, but cludes, throwing down the gauntlet to at the same time a strong diamagnet. Since the scholars of the future. Thomas Gull Meissner-Ochsenfeld’s discovery, a super- conductor must meet two criteria: It must Source: Margrit Wyder: Einstein und Co. – Nobelpreisträger in Zürich; Verlag NZZ libro, conduct electricity without resistance, and it Zürich 2015 Illustration: Aline Telek must expel the magnetic field from its bulk. Translation: University of Zurich After initial successes, superconductor research with metals stagnated. The prob- lem was that metallic compounds become superconductive only at temperatures a ­little above absolute zero, minus 273 de- grees Celsius. They must therefore be cooled with liquid helium, a difficult and expensive procedure. The first superconductive compound produced by Bednorz and Müller, lantha-

www.nobelpreis.uzh.ch/en_mueller.html K. Alex Müller – Nobel Prize in Physics 1987 3/4 K. Alex Müller, 2014. Photo: René Ruis Discovered high temperature superconductivity: K. Alex Müller and J. Georg Bednorz in their lab at IBM in Rüschlikon. Photo: IBM Research - Zurich

In tandem to the Nobel Prize: Physicists K. Alex Müller and J. Georg Bednorz

www.nobelpreis.uzh.ch/en_mueller.html K. Alex Müller – Nobel Prize in Physics 1987 4/4