Physicists observed ultra-slow charge fluctuations in a strange metal

News 2023/03/03

In the quest for new kinds of quantum technology, scientists investigate how quantum mechanics give rise to the exotic materials needed for new devices. Such materials include superconductors and strange metals which do not follow traditional electrical rules. In conventional metals, the resistance increases and then saturates at high temperatures; in strange metals, resistance increases with temperature over a wide temperature range. At ultralow temperatures, strange metals can become superconductors exhibiting zero resistance, which is enticing for physicists on the quest for quantum materials. So, for the first time, a team of physicists studied the charge dynamics of a strange metal YbAlB4, aka Y-ball.  

The team included physicists from the Institute of Physics, University of Tokyo, University of Hyogo in Japan, and Rutgers, Johns Hopkins, and Cincinnati Universities in the United States. They used the fact that Y-ball’s strange metal behavior can be turned off by applying pressure and that the electrons in Y-ball can exist in two valence states: Yb3+ and Yb2+. The pressure-dependent property allowed them to compare Y-ball’s charge dynamics in conventional and strange metal phases using Mossbauer spectroscopy. The spectroscopy provided them with a time-lapse of electric charge dynamics in the form of absorption spectra. In the strange metal state, the Mossbauer spectrum of Y-ball showed two peaks associated with the slow fluctuations of Yb3+ and Yb2+ valence states. When they applied pressure, the Y-ball acted as a conventional metal, and the spectrum reverted to a single peak. The experiments prove that the strange metal state is associated with very slow fluctuations between the Yb3+ and Yb2+ valence states, every nanosecond. 

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