We encounter phase transitions in our everyday lives when we witness water freezing or boiling. Similarly, quantum systems at a temperature of absolute zero also experience phase transitions. The pressure or magnetic field applied to such systems can be adjusted so that these systems arrive at a tipping point between two phases. At this point quantum fluctuations, rather than temperature fluctuations, drive these transitions.
Many fascinating phenomena with promising technological applications in areas such as superconductivity are linked to quantum phase transitions, but the role of quantum fluctuations in such transitions remains unclear. While there have been many advances in understanding the behavior of individual particles such as protons, neutrons, and photons, the challenge of understanding systems containing many particles that strongly interact with one another has yet to be solved.
Now, an international research team led by a group at Osaka University has discovered a clear link between quantum fluctuations and the effective charge of current-carrying particles. This discovery will help researchers uncover how quantum fluctuations govern systems in which many particles interact. One example of such a system is the interaction of electrons at extremely low temperatures. While low temperatures normally cause the resistance in a metal to drop, the resistance rises again at extremely low temperatures due to small magnetic impurities -- this is referred to as the Kondo effect.
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