In Memoriam Karl Alexander Müller

Karl Alex Müller passed away on January 9, 2023, in Zollikerberg near Zurich at the age of 95. It is with great sadness that the scientific community lost an eminent physicist, an IBM Fellow and a Nobel Prize laureate.

Karl Alex Müller was born in Basel on April 20, 1927, the only child of Paul and Irma Müller-Feigenbaum. Soon after his birth, the family moved to Salzburg, Austria, where his father was studying music. A few years later, Alex’s parents separated, and so his mother went with him to Dornach near Basel, to live with her parents. Later both moved to Lugano. His mother died in 1938 when he was 11 years old. He spent the next seven years at the Evangelical College, a boarding school in Schiers, Canton Grisons, only rarely seeing his father, who had remarried and had another child. His time at the school coincided with the outbreak and the end of World War II.

K. Alex Müller’s scientific career started with the studies of physics at ETH Zurich where he was influenced and impressed by the lectures of Prof. Wolfgang Pauli. His diploma work on the Hall effect in grey tin as well as his PhD thesis, which dealt with the paramagnetic resonance in the newly synthesized perovskite SrTiO₃, were both supervised by Prof. Georg Busch. After finalizing his thesis K. Alex Müller entered his professional life as head of the magnetic resonance group at the Battelle Memorial Institute in Geneva. Upon the recommendation of Prof. Ernst Brun he did his habilitation at the University of Zurich in 1962. In view of his high impact on the scientific research, the IBM Research Laboratory Zurich offered him in 1963 the position of a researcher. His leadership skills and strong scientific intuition brought him to lead the physics department in 1971, a position he held until 1985. For almost 15 years his research focused on SrTiO₃ and related perovskites with emphasis on their chemical binding, their ferroelectric and soft-mode properties, and later on their critical and multicritical phenomena at their phase transitions. His outstanding work in the field of perovskite oxides made him famous, and in the community of ferroelectricity he became a worldwide leading expert.

In 1970 he was appointed as titular professor at the University of Zurich. A decisive moment in his career occurred in 1982 when he was nominated IBM Fellow. This enabled him to decide freely and independently about his further research areas – a milestone on his way to the Nobel prize. He started a project with the ambitious goal to synthesize new superconducting materials together with J. Georg Bednorz. The theoretical ideas developed by his friend Prof. Harry Thomas at the University of Basel triggered his interest for complex oxides with Jahn-Teller centers. As a good tandem Alex and Georg made in 1986 the groundbreaking discovery of high-temperature superconductivity (HTS). They found that the resistance of a specific copper oxide vanishes at -238°C (35 K). Both researchers were awarded the 1987 Nobel Prize in Physics for this breakthrough. Based on their seminal work many labs around the world started experimenting with ceramic perovskites, in a bid to reach even higher superconducting temperatures, creating one of the most interesting and researched fields of investigation in physics. Quickly superconductors of the same material class were identified and synthetized, with critical temperatures of up to above 150 K.

Promoted full professor at the University of Zurich, K. Alex Müller continued to work on HTS cuprates developing his favorite viewpoint of a strong electron-lattice interaction based on the formation of polarons or bipolarons to explain the pairing mechanism in this class of materials. In collaboration with researchers from the University of Zurich, PSI, ETH Zurich, and other international institutions novel and unexpected isotope effects on various fundamental properties of HTS cuprates were discovered, confirming his early intuitions.

After achieving the emeritus status as full professor he continued his scientific work at the Physics Institute of the University of Zurich. Very prolific until his advanced age, Alex inspired his colleagues and many generations of students by providing original and critical ideas thanks to his extensive scientific knowledge based on an extraordinary memory. Besides his ingenious scientific achievements and engagements, he was also a dedicated teacher with profound interest in the students and their life. Financial support for students was and still is provided by the K. Alex Müller Foundation.

Recipient of many prizes and awards including several honorary doctorates Alex was also an honorary member of the Swiss Physical Society since 1991.

In addition to his great passion for exact natural sciences, he showed a broad interest in natural philosophical topics and issues related to the Depth Psychology approach of C. G. Jung, as well as in classical music, literature, art, and history.

The legacy of K. Alex Müller lives on, along with the memories of a humble, incredibly talented researcher that left a lasting mark wherever he worked either in Switzerland or in the world.

Chistophe Rossel, IBM Research Europe - Zurich Laboratory
Hugo Keller, University of Zurich

[Released: July 2023|