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Superconductors have attracted much attention due to their huge application potential, and finding new high-temperature superconductors is a goal that the scientific community has been pursuing.

On the evening of July 17th, Beijing time, the research results of Professor Zhao Jun's team from the Department of Physics at Fudan University were published in the latest issue of Nature under the title "Superconductivity in pressurized trilayer La4Ni3O10-δ single crystals".

Screenshots of research results All pictures in this article are provided by Fudan University

Professor Zhao Jun's team successfully grew a three-layer nickel oxide La4Ni3O10 high-quality single crystal sample using high-pressure optical floating zone technology, confirming the pressure-induced bulk superconductivity in nickel oxide, with a superconducting volume fraction of 86%, which means that another new type of high-temperature superconductor has been discovered. The study also found that this type of material exhibits strange metal and unique interlayer coupling behavior, providing a new perspective and platform for people to understand the mechanism of high-temperature superconductivity.

Zhao Jun (third from left in the front row) and his research team members took a group photo

Superconductors refer to materials that have zero resistance and are completely antimagnetic below a certain transition temperature. They can be widely used in power transmission and energy storage, medical imaging, maglev trains, quantum computing and other fields, and have important scientific research and technological application value. Over the years, scientists from all over the world have conducted various forms of in-depth research on the phenomenon of high-temperature superconductivity, but after nearly four decades of efforts, its formation mechanism remains an unsolved mystery.

An important topic in the study of high-temperature superconductivity is to find new high-temperature superconductors. On the one hand, people hope to find clues to understand the mechanism of high-temperature superconductivity from a new perspective, and on the other hand, new material systems may also provide new application prospects.

In the research results published in Nature this time, Zhao Jun's team successfully synthesized a high-quality three-layer nickel oxide La4Ni3O10 single crystal sample. The sample exhibited zero resistance and completely anti-magnetic Meissner effect below the superconducting critical temperature, and the superconducting volume fraction reached 86%, which strongly proved the bulk superconducting properties of nickel oxide.

"This superconducting volume fraction is close to that of copper oxide high-temperature superconductors, which undoubtedly confirms the bulk superconductivity of nickel oxide," said Zhao Jun.

Zhao Jun came to the Department of Physics at Fudan University in 2012 after completing his postdoctoral work at the University of California, Berkeley. His research focuses on neutron scattering in correlated electron systems such as high-temperature superconductors and quantum magnetic materials. He is also engaged in the growth of large-scale, high-quality single crystal samples and the measurement of their thermodynamic and transport properties.

"Breakthroughs in high-temperature superconductivity research are mostly driven by experiments, especially the discovery of new superconductors. So far, there are still many phenomena that cannot be fully explained by existing theories." Zhao Jun introduced, "The growth conditions of nickel oxide single crystal samples are very harsh. It is necessary to maintain high temperature and sharp temperature gradient in a specific high oxygen pressure environment to achieve stable growth of single crystal samples. Since the oxygen pressure window for phase formation is very small, it is easy for nickel oxide layers with multiple components to coexist, and a large number of defects at the vertex oxygen positions are very likely to appear during the growth process, which may be the reason for the low superconductivity content of nickel oxide."

The team used high-pressure optical floating zone technology to grow a large number of samples, constantly looking for and summarizing the rules, and finally successfully synthesized a pure phase three-layer La4Ni3O10 nickel oxide single crystal sample after many failures. Furthermore, the team carried out a series of neutron diffraction and X-ray diffraction measurements to accurately determine the lattice structure and oxygen atomic coordinates and content of the material, and found that there were almost no vertex oxygen defects.

Based on high-quality single crystal samples, the team and collaborators used diamond anvil cell technology to discover the pressure-induced superconducting zero resistance phenomenon of La4Ni3O10. At a pressure of 69 GPa, the superconducting critical temperature reached 30K. According to the diamagnetic data, the superconducting volume fraction of the single crystal sample is as high as 86%, confirming the bulk superconducting properties of nickel oxide.

The research results also finely depict the superconducting phase diagram of the La4Ni3O10 system under pressure, and clarify the relationship between charge density wave/spin density wave, superconductivity, strange metal behavior and crystal structure phase transition in the phase diagram. The results show that nickel oxide superconductivity may have a different interlayer coupling mechanism from copper oxide superconductivity, providing important insights into the mechanism of nickel oxide superconductivity and an important material platform for exploring the complex interactions between spin order-charge order, flat band structure, interlayer correlation, strange metal behavior and high-temperature superconductivity.

In the next step, Zhao Jun’s team will continue to focus on major issues in the field of high-temperature superconductivity, explore the internal connections and mechanisms of high-temperature superconductors in different systems, and understand and discover higher-performance high-temperature superconductors.

Professor Zhao Jun of Fudan University, researcher Guo Jiangang of the Institute of Physics, Chinese Academy of Sciences, and Zeng Qiaoshi of the Beijing High Pressure Science Research Center are the co-corresponding authors of the paper. Postdoctoral fellow Zhu Yinghao of the Department of Physics, Fudan University, doctoral student Peng Di of the Beijing High Pressure Science Research Center, Zhang Enkang of the Department of Physics, Fudan University, associate professor Pan Bingying of the Ocean University of China, and engineer Chen Xu of the Institute of Physics, Chinese Academy of Sciences are the co-first authors.