A pioneer in the research of mesoscopic physics and statistical mechanics of random systems.
Yoseph (Joe) Imry was born in Tel Aviv, Israel, in 1939. He earned his B. Sc. and M. Sc. from the Hebrew University in Jerusalem and completed his Ph. D. research at the Weizmann Institute under the supervision of Prof. Israel Pelach, founder and the first CEO of the Soreq Nuclear Research Center. After two years of post-doc at Cornell University, he joined Tel-Aviv University and in 1987 moved to the Weizmann Institute of Science in Rehovot, Israel.
Imry, the 2016 Wolf prize laureate for Physics, was a trailblazer in the studies of statistical physics of random systems and quantum phenomena in mesoscopic physics. His study with S.K. Ma of the effect of quenched randomness on phase transitions was an example of insightful analysis. While initially applied to magnetic systems, the “Imry-Ma argument” has been extended to a broad range of phase transitions. The essence of the argument lies in a comparison between the free energy associated with flipping spin domains and the change in free energy of the accompanying domain walls. The argument led to the conclusion that in low dimensions an arbitrarily weak random field excludes long-range spin ordering.
Fascinated by what were then new fabrication technologies of sub-micron electronic devices, Imry turned his attention to the study of quantum phenomena in mesoscopic systems – small devices at the borderline between the macroscopic and the atomic realms. He was among the pioneers of the field, making several seminal discoveries. A discussion of a portion of his ideas is summarized in his own book: Introduction to Mesoscopic Physics. Arguably, the most striking of these was the prediction of persistent currents in mesoscopic metallic rings threaded by magnetic flux. At that time, in the early eighties, it has long been realized that superconducting rings carry persistent currents but the prediction that normal metal rings, even imperfect ones, may carry such currents was a great surprise. Imry, together with Rolf Landauer and Markus Büettiker, realized that if the ring was small enough for electrons to maintain their phase coherence while encircling it the magnetic flux could induce a current-carrying state also in thermodynamic equilibrium. The quantum mechanical nature of this phenomenon was explicitly manifested in its flux-periodicity, shedding light on the relationship between persistent currents and the Aharonov—Bohm effect. This counter-intuitive prediction was initially greeted with skepticism until confirmed experimentally.
Going beyond equilibrium properties, Imry together with colleagues, students and post-docs, examined the way phase coherence affects transport properties of mesoscopic systems, unraveling principles that have since become “bread and butter” of the field. Ohm's law for resistors in series and in parallel had to be revised for phase-coherent electrons and thermo-electric effects were shown to display a quantum signature. Adopting the Landauer approach Imry elucidated the difference between two-terminal and four-terminal measurements and more generally showed that measured transport properties, including fundamental ones such as electrical and thermal resistances, depend in phase-coherent systems on the precise experimental configuration.
The development of mesoscopic physics exposed several fundamental questions and Imry made important contributions towards their resolution. Notable among those were the fluctuations in electric conductance of mesoscopic samples differing in microscopic details of their disorder and the relation of these universal fluctuations to Random Matrix Theory and Quantum Chaos. Other examples include the description of processes in which quantum coherence is lost due to interactions of interfering waves with their environment and the slow relaxation and aging of electronic Coulomb glasses. In the picture developed in the latter study, aging reflected processes of varying relaxation rates corresponding to adjustments of domains whose size increased with decreasing rate. This picture provided an accurate universal description of aging in diverse physical systems.
Besides his direct scientific contributions, Imry has contributed significantly to the condensed matter physics community, both within Israel and internationally. He was most influential in advancing experimental research into sub-micron electronic samples. Most notably, he was the driving force behind the foundation of the Sub-Micron Physics Center at the Weizmann Institute of Science. On a personal level, he was an advisor and a mentor to dozens of Israeli and international scientists. Those who were fortunate to interact with him were influenced by his solid principles – the importance of theory being closely and interactively relevant to experiments, the importance of backing up mathematical details by clear and lucid physical thinking, and the essential role of both passion and humor when discussing physics.