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Superconductors have attracted much attention due to their huge application potential

Searching for new high-temperature superconductors

It is the goal pursued by the scientific community

Nature just published the latest results of Fudan University

Another new type of high-temperature superconductor has been discovered!

Department of Physics, Fudan University

Professor Zhao Jun's team

Successfully grown using high-voltage optical floating zone technology

Three-layer nickel oxide La4Ni3O10

High quality single crystal samples

provedPressure-induced

Bulk superconductivity

(bulk superconductivity)

Its superconducting volume fraction reaches 86%

The study also found that this type of material showed

Strange metals and unique interlayer coupling behavior

Help people understand the mechanism of high-temperature superconductivity

Provides new perspectives and platforms

On the evening of July 17th, Beijing time, the research results were published in the latest issue of Nature under the title "Superconductivity in pressurized trilayer La4Ni3O10-δ single crystals". At the same time, Nature recommended and introduced the article in the "News & Views" column under the title "The search for superconductivity widens".

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

Can nickel oxide be superconducting?

Physics puzzle has answer

Superconductors refer to materials that have zero electrical 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. So far, 10 scientists have won the Nobel Prize for superconductivity research.

In 1911, Dutch physicist Heike Kamerlingh Onnes first discovered superconductivity in mercury (Hg). When he cooled mercury to about 4 K (K = -269.15°C), the resistance of mercury suddenly disappeared and became zero. For a long time thereafter, scientists believed that only conventional metals and simple alloys such as mercury, lead, and aluminum could exhibit superconductivity at extremely low temperatures.

It was not until 1986 that Johannes Georg Bednorz and Karl Alexander Müller discovered high-temperature superconductivity in lanthanum barium copper oxide (La-Ba-Cu-O), with a critical temperature as high as 30 K. Later, scientists from many countries, including Chinese scientists, raised the superconducting critical temperature to the liquid nitrogen temperature range (77 K) and even exceeded 130 K.

The discovery of high-temperature superconductivity has broken people's perception that superconductivity can only exist at extremely low temperatures.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.

Nickel is right next to copper in the periodic table, and nickel oxide is considered to be one of the important candidate materials for achieving high-temperature superconductivity.But after decades of research, people have found that the conditions for achieving superconductivity in nickel oxide are very harsh.

In 2019, the Nd0.8Sr0.2NiO2 system with infinite layers of NiO2 surfaces was reported to have superconductivity, with a transition temperature of about 5-15 K. However, superconductivity in this type of system can only exist in thin film samples, and bulk materials cannot achieve superconductivity.

In 2023, Chinese scientists discovered pressure-induced high-temperature superconductivity in nickel oxide La3Ni2O7 with a double-layer NiO2 surface structure, and the superconducting critical temperature reached 80 K, further raising the superconducting transition temperature of nickel oxide to the liquid nitrogen temperature range. However, the superconducting volume fraction of this material is low, and it is easy to show filamentary superconductivity, and it is difficult to form bulk superconductivity. Therefore, it is very important to find a new superconducting system, increase the superconducting volume fraction, and achieve bulk superconductivity.

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.

Providing a new perspective and platform for superconducting research

Committed to discovering higher performance high-temperature superconductors

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."

teamUsing high-pressure optical floating zone technologyAfter growing a large number of samples and constantly searching for and summarizing the rules, the team finally succeeded in synthesizing 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.The material's lattice structure and oxygen atomic coordinates and content were precisely determined, and it was found that there were almost no vertex oxygen defects.。

(a) Photo of La4Ni3O10-δ single crystal sample; (b) Neutron and X-ray single crystal diffraction data; (c) Evolution of lattice structure under pressure

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 30 K. 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.

Measurement results of resistance and magnetic susceptibility of La4Ni3O10-δ single crystal samples

Unlike the infinite layer and double layer nickel oxide NiO2 surfaces with the same chemical environment, the unique sandwich structure formed by the three-layer structure allows the outer and middle NiO2 surfaces to have different chemical environments, which can produce different magnetic structures, electron correlation strengths, charge concentrations, and even superconducting pairing strengths in the inner and outer NiO2 surfaces, which provides more possibilities for the regulation of superconductivity. This structure alsoProvides a unique platform for understanding the role of interlayer coupling and charge transfer in the formation of high-temperature superconductors。

In addition, the three-layer nickel oxide has stronger antiferromagnetic order than the infinite layer and bilayer systems, which provides a good opportunity to understand the relationship between spin correlation and spin fluctuations and the high-temperature superconductivity mechanism of nickel oxide, while spin fluctuations are widely believed to play a key role in copper oxide superconducting pairing.

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.

Phase diagram of La4Ni3O10-δ under pressure

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 of the Chinese Academy of Sciences, and Zeng Qiaoshi of the Beijing High Pressure Science Research Center are the co-corresponding authors of the paper. Zhu Yinghao, a postdoctoral fellow in the Department of Physics of Fudan University, Peng Di, a doctoral student in the Beijing High Pressure Science Research Center, Zhang Enkang of the Department of Physics of Fudan University, Associate Professor Pan Bingying of the Ocean University of China, and Engineer Chen Xu of the Institute of Physics of the Chinese Academy of Sciences are the co-first authors. This research was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology, the Shanghai Science and Technology Commission, the Beijing Natural Science Foundation, and the Shandong Natural Science Foundation. Some of the data for this research were collected at large scientific platforms such as the Chinese Academy of Sciences' Comprehensive Extreme Conditions Experimental Facility, the Oak Ridge National Laboratory in the United States, and the Shanghai Synchrotron Radiation Light Source.

Article link

https://www.nature.com/articles/s41586-024-07553-3

Editorial

School Media Center

Word

Yin Menghao Ding Chaoyi

picture

Photo provided by the interviewee

Editor

Yin Menghao

Qiu Jiexin

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