USTC has made significant discoveries in the study of caged superconductors

At 0:00 on November 24, Beijing time, the academic journal Nature published online the latest discovery of Professor Wu Tao and others of the team of Academician Chen Xianhui of the University of Science and Technology of China, using nuclear magnetic resonance spectroscopy technology under high pressure to observe a new type of charge ordered state induced by pressure in the caged superconductor cesium vanadium antimony, and found that the charge ordered state and the superconducting state presented a competitive phase diagram similar to a high-temperature superconductor under pressure. The result is another major discovery by Chen’s team following a report on the new electron nematic phase in caged superconductors in Nature in February this year.

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Group photo of the team of Academician Chen Xianhui (middle) of the University of Science and Technology of China (second from right, Wu Tao) and Dai Rui

In the study of unconventional superconductors, it has been found that there is always an intricate competition between superconducting states and competing electronic states, and they can also be intertwined with each other to further form novel superconducting states. Exploring the complex evolutionary phenomena and physical mechanisms between superconducting states and competing electronic states is one of the key issues in the current superconductivity research field.

Caged superconductor is a new type of superconducting material, which has exhibited many strange physical properties due to its special geometric structure and non-local electron association, and is considered to be a new quantum material with important scientific research value. In previous research, Chen’s team found that under pressure, there was anomalous competition between superconducting states and charge density wave states in caged superconductors, indicating that there may be competing electron sequences that have not yet been discovered.

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Academician Chen Xianhui, Professor Wu Tao and students discussing the topic experiment Photo by Dai Rui

Wu Tao has been working on the use of NMR spectroscopy to study competitive electron sequences in high-temperature superconductors for many years, and has established a NMR experimental platform with comprehensive extreme conditions (strong magnetic field, extremely low temperature and ultra-high pressure) at the University of Science and Technology of China. In this work, Wu Tao and others carried out nuclear magnetic resonance studies of the caged superconductor cesium-vanadium antimony under pressure, and the results showed that when the hydrostatic pressure was higher than about 06,000 atmospheres, the superconductivity of the system was violently suppressed, and at the same time a new charge density wave state evolved, similar to a competing electron sequence-charge fringe sequence previously found in high-temperature copper oxide superconductors. When the pressure is further increased to about 20,000 atmospheres or more, the new charge density wave state is completely suppressed, and the superconducting transition temperature is also raised to the highest value. These results show that the new charge order state has a strong competition with the superconducting state, which is a new competing electron sequence. In addition, the research team also observed the phenomenon of charge fluctuations caused by electron correlation effects in caged superconductors and possible unconventional superconductivity under pressure.

The above experiments reveal novel electron correlation effects and rich evolutionary phenomena in caged superconductors, which provides a new opportunity for understanding the complex interaction mechanism between superconducting states and competing electron states, and also provides a new direction for exploring novel superconducting states in caged superconductors. In addition, Wu Tao pointed out: “From the perspective of electron-electron association interaction, although caged superconductors have weak association interactions, competing electron sequences similar to high-temperature superconductors are observed, which indicates that there may be a new electron-electron association effect in caged superconductors, but the specific physical mechanism needs to be further explored.” (Source: Wang Min, China Science News)

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