Alexander Müller (1927–2023)

In 1986, Alexander Müller and his student Georg Bednorz discovered high-temperature (high-T_c) superconductivity. Only a year later, their discovery earned them the 1987 Nobel Prize in Physics. Superconductivity, in which all electrical resistance disappears below a critical temperature, had been known since 1911, but mainly in metals and alloys cooled to within a degree or two of absolute zero. Müller, who has died aged 95, demonstrated the transition to superconductivity at a temperature of 35 K (35 °C above absolute zero) in a class of ceramic known as cuprates, raising the tantalizing possibility of frictionless power distribution, levitating trains and other applications.

The physics world, initially sceptical, was gripped by excitement. At the American Physical Society’s March 1987 meeting, later dubbed the ‘Woodstock of physics’, in reference to the 1969 music festival, more than 2,000 physicists crammed into a hotel ballroom to hear a panel discuss the new superconductors. By this time, others had found related materials with transition temperatures close to 100 K. High-T_c superconductivity has since been used in magnetic resonance imaging systems and in other specialized applications — yet theorists continue to seek a satisfactory explanation for how it works.

First room-temperature superconductor excites — and baffles — scientists

Born in Basel, Switzerland, in 1927, Müller caught the science bug in childhood, when his mother gave him a vacuum-tube radio kit. At the Swiss Federal Institute of Technology in Zurich, he attended seminars given by the Nobel-prizewinning theoretical physicist Wolfgang Pauli. For his doctoral thesis under Georg Busch, he used electron paramagnetic resonance spectroscopy to study the electrical and magnetic properties of a variety of solids.

In 1958, Müller moved to the Geneva branch of the Battelle Institute, a non-profit industrial research and development organization headquartered in Columbus, Ohio. He studied radiation damage in graphite, in response to the 1957 accident at the Windscale nuclear reactor in the United Kingdom. Partly owing to damage in its graphite moderator, the reactor had overheated and caught fire, releasing a radioactive plume across Europe. Müller’s work on neutron-irradiated graphite, published in Physical Review in 1961 (K. A. Müller Phys. Rev. 123, 1550–1552; 1961), caught the attention of the director of IBM Research Zurich in Rüschlikon. He lured Müller away from Geneva in 1963 to work on solid-state problems relevant to IBM’s investment in digital computing.

Müller spent the rest of his career at IBM Rüschlikon. He established himself as a world-leading expert on perovskites — oxides with a distinctive, symmetrical crystal structure that makes them suitable for a wide range of engineering applications, including microelectronics and solar cells.

High-temperature superconductivity at 25: Still in suspense

Müller took a parallel appointment as a professor at the University of Zurich in 1970, and became director of the physics division at IBM Rüschlikon in 1973. During a two-year secondment to IBM’s Thomas J. Watson Research Center in Yorktown Heights, New York, in 1978, he seized on superconductivity as a promising research area — made more tractable by emerging work in critical phenomena, such as phase transitions. After his return to Zurich, he was named an IBM Fellow and given freedom to pursue independent research. He took up high-T_c superconductivity in earnest, and, in 1983, began his collaboration with Bednorz, who shared his fascination with perovskites.