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Karl Alexander Müller

In their search for new superconductors, Swiss theoretical physicist Karl Alexander Müller and his young colleague, J. Georg Bednorz, abandoned the metal alloys typically used in superconductivity research in favor of a class of oxides known as perovskites.

Karl Alexander Müller

The unusual direction of their work resulted in an important breakthrough in 1986 — superconductivity at a higher temperature than ever achieved before. When Müller and Bednorz announced their discovery, it caused such a stir in the scientific community that soon laboratories around the globe were experimenting with ceramic perovskites in hopes of attaining even higher superconducting temperatures. The flurry of interest did not escape the attention of the Nobel Prize Committee, which awarded the Nobel Prize in Physics to Müller and Bednorz in 1987.

Born in Basel, Switzerland, Müller was related to prominent Swiss chocolate makers. Shortly after his birth, he moved to Salzburg, Austria, so that his father could continue his study of music. Later he returned to Switzerland, living with his mother in Dornach and then Lugano until her death in 1938. Müller was displaced yet again when he and his father relocated to Schiers, a Swiss town near the Austrian border. Müller attended the Evangelical College there and became intrigued by radio and electronics. Although he contemplated becoming an electrical engineer, one of his teachers believed he would make a great physicist and encouraged him in that direction.

After graduating in 1945, Müller completed mandatory service for the Swiss military before continuing his education at the Swiss Federal Institute of Technology (ETH) in Zürich. Again he considered engineering, but instead joined the Physics and Mathematics Department, taking classes taught by Wolfgang Pauli and other leading scientists. A particularly strong influence on Müller, Pauli was a Nobel laureate who suggested the existence of a fourth quantum number and developed the exclusion principle.

Müller completed the equivalent of a master’s degree in 1952. His focus had by then turned to solid-state physics, and by the time he received his doctorate in 1958 his primary research interest was perovskites, the ceramics with which he would make his great contribution to science. For his doctoral thesis, Müller studied the ceramic strontium titanium oxide. His first job after graduation was managing a magnetic resonance research group at the Battelle Memorial Institute in Geneva. But in 1963, offered a position at the IBM Zürich Research Laboratory, he had the opportunity to work with perovskites again. Müller had first come to the attention of lab management while lecturing at the University of Zürich in 1962.

Müller spent many years investigating the various properties of perovskites at IBM. In 1973 he became director of the lab’s physics division, and in the post made many crucial hires. In the late 1970s he brought on Gerd Binnig, who a few years later developed the scanning-tunneling microscope with his colleague Heinrich Rohrer. Binnig and Rohrer shared part of the Nobel Prize in Physics in 1986. Ten years after becoming physics director, Müller added Bednorz, then a recent ETH graduate, to his group. Bednorz had already begun extensive work with ceramic oxides (his doctoral thesis focused on the production and characterization of perovskites), having been encouraged by Müller while visiting the lab as a graduate student.

In their research together, Müller chiefly worked in a theoretical capacity while Bednorz did the hands-on making and testing of ceramics. For the first few years, the pair had little success developing practical superconducting oxides. Although some of the compounds made under Müller’s direction had become superconductors, they only achieved this state at temperatures far below the then-record high of 23 K. Their aim was to find a compound that would be superconductive at a higher temperature, making superconductor-based technologies a reality. Then one day Bednorz happened to read about a compound of copper and oxygen with trace amounts of barium and lanthanum produced by a group of French scientists. Although the group had not carried out any superconductivity testing, Bednorz had a feeling the compound could be exactly what he and Müller needed.

In 1986, after experimenting with different ratios of the elements, a sample prepared by Bednorz that was similar to the French compound observably lost its electrical resistance at 35 K, apparently making it the highest temperature superconductor known at the time. However, because they had not yet tested the sample for the Meissner effect (after loss of electrical resistance the second defining characteristic of a superconductor), Müller and Bednorz could not be sure they had achieved superconductivity. Not wanting to delay publication, Müller and Bednorz announced their findings in April 1986 in the German journal Zeitschrift für Physik. The title of their article, "Possible High [Transition Temperature] Superconductivity in the Ba-La-Cu-O System," projected a sense of reserve and, as Müller and Bednorz anticipated, their claims were greeted with substantial skepticism. Other research groups, however, quickly confirmed their results and showed that the compound did exhibit the Meissner effect, proving it was a true superconductor. An international race to find perovskite superconductors with even higher transition temperatures ensued. It was not long before scientists could produce ceramics with high enough transition temperatures that they could be cooled with liquid nitrogen, rather than the more expensive liquid helium previously required to achieve superconductivity.

Many scientific societies and institutions swiftly recognized the groundbreaking achievement. In addition to the Nobel Prize, Müller received the Marcel-Benoist Prize, the Thirteenth Fritz London Memorial Award, the Dannie Heineman Prize, the Hewlett-Packard Europhysics Prize, the American Physical Society International Prize for New Materials Research and the Minnie Rosen Award, among others. Numerous universities from around the world bestowed honorary degrees upon him as well. Despite the astounding attention, Müller steadfastly continued his work in superconductivity research at IBM for many years. In 1982 IBM made him a Fellow and in 1987 he ended his management role at the laboratory. Müller officially retired from IBM in 1992.