| K. Alex Müller | |
|---|---|
| Name | K. Alex Müller |
| Birth date | 1927-04-20 |
| Birth place | Basel, Switzerland |
| Death date | 2023-01-09 |
| Nationality | Swiss |
| Fields | Physics, Solid-state physics, Condensed matter physics |
| Workplaces | IBM, ETH Zurich, University of Zurich |
| Alma mater | ETH Zurich |
| Known for | Discovery of high-temperature superconductivity in cuprates |
| Awards | Nobel Prize in Physics |
K. Alex Müller
K. Alex Müller (20 April 1927 – 9 January 2023) was a Swiss physicist notable for his pioneering work on superconductivity, particularly the discovery of high-temperature superconductivity in copper oxide ceramics. His research bridged experimental solid-state physics and aspects of quantum mechanics relevant to macroscopic quantum phenomena, influencing quantum materials research and technologies such as quantum computing and superconducting electronics.
K. Alex Müller was born in Basel and grew up in a family with academic interests, which fostered his early inclination toward experimental science. He studied electrical engineering and physics at the ETH Zurich, where he completed a diploma and later a doctorate under supervision that emphasized low-temperature and dielectric measurements. During his formative years at ETH Zurich he became versed in experimental techniques such as cryogenics, precision resistivity, and dielectric spectroscopy, establishing skills later applied to studies of superconductivity and correlated-electron systems.
After completing his doctorate, Müller worked in industry and research laboratories, including a period at Brown, Boveri & Cie and at IBM's research center in Rüschlikon (later IBM Zürich Research Laboratory), where he engaged in investigations of dielectric materials and ferroelectrics. In the 1960s and 1970s he held positions at the University of Zurich and collaborated with groups at ETH Zurich, developing expertise in cryogenic instrumentation and materials synthesis. Müller's career pivoted in the 1980s toward oxide ceramics; he and his long-term collaborator Georg Bednorz focused on transition-metal oxides, conducting systematic searches for new superconducting phases informed by solid-state chemistry and band-structure considerations from band theory and electron correlation physics.
Müller's principal contribution was the experimental discovery, with Georg Bednorz, of superconductivity in doped copper-oxide perovskites (cuprates) at temperatures far above previously established limits for conventional superconductors. This finding challenged the applicability of the conventional Bardeen–Cooper–Schrieffer theory (BCS theory) to high-transition-temperature (high-Tc) materials and stimulated theoretical work invoking strong electron correlations, antiferromagnetism, and unconventional pairing symmetries (e.g., d-wave pairing). The discovery established a new class of quantum many-body systems in which collective phenomena—coherence, phase stiffness, and quantum fluctuations—manifest at elevated temperatures, with direct relevance to macroscopic quantum effects and the development of superconducting quantum devices such as SQUIDs and qubits based on Josephson junctions.
Müller and Bednorz's 1986 experiments targeted lanthanum-based cuprate ceramics La2-xBaxCuO4 variants, using careful sample preparation, doping control, and low-temperature resistivity and magnetization measurements to detect superconducting transitions above 30 K. Subsequent rapid advances by the community extended critical temperatures beyond 90 K in yttrium-barium-copper-oxide (YBa2Cu3O7) and other layered cuprates, driven by techniques for thin-film growth (e.g., pulsed laser deposition), single-crystal synthesis, and spectroscopic probes such as angle-resolved photoemission spectroscopy (ARPES), neutron scattering, and muon spin rotation (μSR). Müller's work stimulated experimental programs that combined transport, thermodynamic, and spectroscopic measurements to elucidate the pseudogap, Fermi-surface reconstruction, and pairing symmetry—central topics linking material-specific experiments to models in quantum many-body physics like the Hubbard model and t-J model.
The discovery of high-Tc superconductivity transformed research priorities in condensed matter physics and spawned the interdisciplinary field of quantum materials, encompassing phenomena such as unconventional superconductivity, topological phases, and correlated-electron behavior. Practical implications include development of superconducting magnets, lossless power applications, and components for superconducting electronics. In the context of quantum technologies, cuprate superconductors and the broader class of correlated oxides provided testing grounds for coherent quantum phenomena at elevated temperatures and inspired device concepts for superconducting qubits, rapid single-flux quantum (RSFQ) logic, and hybrid quantum systems coupling superconductors with semiconductors or spintronics elements. Müller's legacy also catalyzed materials-by-design approaches combining synthesis, measurement, and theory to seek new quantum phases.
Müller shared the Nobel Prize in Physics in 1987 with Georg Bednorz for their discovery of superconductivity in ceramic materials, an accolade that underscored the importance of their work to both fundamental quantum physics and potential applications. He received numerous honors and maintained collaborations with institutions such as ETH Zurich, the University of Zurich, and international laboratories including CEA Saclay, Los Alamos National Laboratory, and Max Planck Institute for Solid State Research. His role as a mentor and collaborator influenced experimentalists and theorists working on quantum criticality, electron pairing mechanisms, and emergent phenomena in correlated materials, linking his empirical approach to broader efforts in the quantum physics community to harness material complexity for quantum devices.
Category:Swiss physicists Category:Nobel laureates in Physics