Thomas Kuhn’s philosophy of scientific revolutions popularised the idea of paradigm shifts. What his theory doesn’t capture, however, is the historical and biographical wealth of paradigm shifts.
By virtue of being united in character, in Kuhn’s description, they reveal an otherwise elusive Ariadne’s thread in these watershed moments in the history of science. It’s possible to see, for example, in Dan Shechtman’s discovery of quasicrystals in the early 1980s parallels to reports in 2018 that scientists at the Indian Institute of Science (IISc), Bengaluru, had discovered room-temperature superconductivity, and in fact to the discovery of high-temperature superconductors in the late 1980s.
This last one was a milestone in many ways. For more than a decade until 1986, the highest temperature at which a material became superconducting – that physicists were aware of – was 23 K (-250.10º C). This changed in 1986 when Karl Alexander Müller and J. Georg Bednorz discovered lanthanum barium copper oxide (LBCO) becoming superconducting at 35 K. In numbers this was only a 12 K jump, but in the history of physics, it was the fall of a barrier that physicists had taken to mean was a field nearing full understanding. As if to garnish the moment, LBCO was also a ceramic – materials that scientists at the time considered to be insulators.
Müller passed away on January 9 this year at the age of 95. He was born in Basel in April 1927. He finished college in 1945, served briefly in the Swiss military as part of his civilian obligations, and then enrolled at ETH Zurich. One of his professors here was Wolfgang Pauli, of Pauli’s exclusion principle fame and one of the knaben of the knabenphysik. Müller completed his PhD in 1958 and joined IBM five years later, where he continued work he had started for his PhD, on materials called perovskites.
After his and Bednorz’s discovery, but before the end of the year, research groups in Tokyo and Texas, led respectively by Shoji Tanaka and Paul C.W. Chu, had independently confirmed it. Chu et al. also discovered yet another cuprate high-temperature superconductor, yttrium barium copper oxide (YBCO), which transitioned at 93 K.
Several things happened at this point.
Obviously the community of condensed-matter physicists was excited. In the words of Douglas Finnemore, “The discovery of superconductivity in the cuprate class of conducting oxides brought a flash of sunlight on one of the fields … that many of us had thought was rather mature and fairly well understood”.
The American Physical Society made a last-minute addition to its annual meeting in March 1987 for Müller and the others to present their findings, in light of the YBCO finding. The event has since been called the “Woodstock of physics”. More than 2,000 physicists gathered at the New York Hilton, the venue, two hours in advance, spilling over the seats into the aisles and outside, where TV screens displayed the proceedings that lasted from 7.30 pm until 3.15 am.
In 1987, Müller and Bednorz received the Nobel Prize for physics for their discovery. It was a record for the shortest time between a contribution to physics and receiving the award. Recall that a characteristic requirement to win a Nobel Prize is that your work should have had demonstrable benefits to humankind. This is testament to the obvious significance of the work of Müller, Bednorz, Chu, Tanaka, etc. In the same year, researchers in Tsukuba, led by Hiroshi Maeda, discovered the first so-called triple-digit superconductor: bismuth strontium calcium copper oxide (BSCCO, a.k.a. bisko), which transitioned at 107 K.
Apart from remaking history, higher and higher transition temperatures also spoke to a crucial engineering challenge. In 1911, the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in mercury because he had previously invented a technique to cool materials to extremely low temperatures. Mercury transitions at 4.2 K. Materials that transition at 4.1 K or below need to be cooled using liquid helium, whose boiling point is 4.15 K. Materials that transition below 77 K can on the other hand be cooled using liquid nitrogen, which is easier to handle.
LBCO broke the liquid-helium barrier whereas YBCO and BSCCO broke the liquid-nitrogen barrier. The latest goal on this road is to find a room-temperature superconductor, which is why the IISc reports in 2018 raised so much interest.
Then again, while it has been more than three decades since the discovery of these marvellous copper-oxides, physicists are still working to understand their microscopic structure and to develop a theory that can explain why they superconduct. This is harder than it sounds despite the availability today of advanced probing and modelling techniques. Researchers are also discovering new superconductors that oppose existing theories in little ways. For example, a group at the Tata Institute of Fundamental Research, Mumbai, reported in 2016 that elemental bismuth superconducts at a bristling 0.00053 K, in circumstances that the relevant theory couldn’t explain.
Defiance is an essential part of scientific revolutions. Shechtman famously defied Linus Carl Pauling to stand by his data, which showed the existence of a kind of crystal that Pauling had deemed impossible. In similar vein, as “news of the discovery started to spread” in 1986, Bednorz recalled two decades later, “we experienced mixed reactions ranging from silent scepticism to polite (cautious) congratulations”, leading ultimately to full-blown excitement when Tanaka and Chu reported their independent confirmation.
Defiance is special because it challenges the idea of scientists bravely following theoretical predictions to often unlikely conclusions, although this is as much a comment on the social conditions in which scientists operate as on how they create and improve theories.
For example, though they eventually found something that threw the gates of superconductor physics wide open, Müller and Bednorz weren’t exactly groping in the dark. They had expected to find a high-temperature superconductor based on predictions of the BCS theory of superconductivity and something called the Jahn-Teller effect. ‘BCS’ stands for Bardeen-Cooper-Schrieffer, three physicists who developed the first microscopic theory to explain superconductivity in metallic materials that transitioned at a low temperature, like mercury. But as historian of science Gerald Holton noted in the 1998 edition of The Scientific Imagination, both the BCS theory and the Jahn-Teller effect were subsequently found to have “little to do” with high-temperature superconductivity.
Yet, as Holton continued, Müller also wasn’t sure if they would succeed. He worked at IBM in Rüschlikon, Switzerland, was made an IBM fellow in 1982 and recruited Bednorz in 1983. IBM published an obituary on the day of Müller’s passing saying, “Despite his managerial role, Müller still found time to do research. He started a project with the ambitious goal to synthesise new superconducting materials together with J. Georg Bednorz.” Yet Müller didn’t tell his managers at the time nor others that he was working on superconductivity. Among other reasons, he hoped that if he and Bednorz hit a dead-end, they could quietly bury their work “in order to not jeopardise Bednorz’s career”.
Something similar happened when Dov Levine discovered quasicrystals around the time Shechtman had, but Paul Steinhardt advised caution before publishing his findings. At least one physicist also thought Müller and Bednorz were “crazy” to look for an oxide high-temperature superconductor.
The romantic notion of a scientific revolution, together with its promise to beget futuristic new technologies, belies its profound messiness, especially the risks its central actors assume when they stand by their findings. Then again, to adapt the wisdom of Subrahmanyan Chandrasekhar, greatness among scientists shows itself when they know which questions are worth answering – and which risks are worth taking. Müller, in this regard, came out on top.
- Alex Müller was born in Basel in April 1927. He finished college in 1945, served briefly in the Swiss military as part of his civilian obligations, and then enrolled at ETH Zurich. One of his professors here was Wolfgang Pauli, of Pauli’s exclusion principle fame and one of the knaben of the knabenphysik. Müller completed his PhD in 1958 and joined IBM five years later, where he continued work he had started for his PhD, on materials called perovskites. He passed away on January 9 this year at the age of 95.
- For more than a decade until 1986, the highest temperature at which a material became superconducting – that physicists were aware of – was 23 K (-250.10º C). This changed in 1986 when Karl Alexander Müller and J. Georg Bednorz discovered lanthanum barium copper oxide (LBCO) becoming superconducting at 35 K.
- In 1987, Müller and Bednorz received the Nobel Prize for physics for their discovery.