08,12,2026 8 views
【Instrument Network R&D News】High temperature superconductivity is an important direction for the development of efficient power transmission and high-performance electronic devices in the future, but its microscopic mechanism remains the "crown mystery" of condensed matter physics.
On the evening of August 12th Beijing time, Professor Zhang Yuanbo's team and collaborators from the Department of Physics at Fudan University published research results in Nature titled "Superconducting 2D cuprate with a single CuO ₂ plane", successfully thinning copper based high-temperature superconductors to only contain one superconducting plane - a single CuO ₂ plane.
This' extreme operation 'not only confirms the two-dimensional nature of high-temperature superconductivity, but also discovers strange' anomalous metal states' and quantum critical phenomena at the critical point of superconducting insulator transition, providing a new quantum experimental platform for studying the mechanism of high-temperature superconductivity
Approaching the physical limit: the leap from "double-layer" to "single-layer"
Superconductors are a type of material with zero resistance and complete diamagnetism at a specific transition temperature. They can be widely used in fields such as power transmission and energy storage, medical imaging, maglev trains, quantum computing, etc., and have important scientific research and technological application value.
In 1986, J. Georg Bednorz and K. Alex M ü ller discovered high-temperature superconductivity in La-Ba-Cu-O, with a critical temperature of up to 30 K (K is the thermodynamic temperature unit Kelvin, 30 K=-243.15 ℃). This achievement won the Nobel Prize in Physics in 1987. Subsequently, scientists have conducted in-depth research on copper based high-temperature superconductors and have developed dozens of material systems. Although these copper based high-temperature superconductors have different chemical compositions and superconducting critical temperatures, they all share a common feature - superconductivity arises from an extremely thin atomic level two-dimensional copper oxygen plane.
However, according to traditional physics theory, obtaining an "ordered state" like superconductivity in a two-dimensional world is highly unstable and easily disrupted by thermal fluctuations. Why does high-temperature superconductivity exist stably on a two-dimensional copper oxygen surface? This is the key to understanding the mechanism of high-temperature superconductivity.
The most direct strategy to confront this issue is to make the material extremely thin, even reducing it to atomic level thickness, and observe the changes in superconductivity. However, the atomic layer of copper oxide is extremely fragile and susceptible to the influence of air and processing technology. The oxygen content is also difficult to stabilize and precisely control, which poses great challenges to the preparation and measurement of materials that maintain their intrinsic properties.
In 2019, Zhang Yuanbo's team and collaborators prepared single-layer Bi2Sr2CaCu2O8+δ and provided direct experimental evidence for the first time, proving that single-layer copper based superconductors under two-dimensional limits have the same superconducting properties as bulk copper based superconductors, revealing the two-dimensional nature of high-temperature superconductivity. The research results were published in Nature. This time, the team went further and successfully prepared a single layered Bi2Sr2CuO6+δ (Bi2201) two-dimensional copper oxide superconductor containing only a single CuO ₂ surface based on previous research.
We have for the first time advanced the thickness of copper oxide from a bilayer to a true monolayer structure, achieving the ultimate verification of the superconducting properties of copper oxide. The measured data strongly supports the view that 'high-temperature superconductivity of copper oxide is a strong two-dimensional phenomenon', providing key experimental evidence for this long-term hypothesis, "said Zhang Yuanbo.
Independent research and development, creating a scientific research tool for "in-situ regulation"
To prepare and measure extremely thin atomic level two-dimensional planes, several experimental difficulties need to be overcome, such as material fragility, susceptibility to air and processing technology, and difficulty in stable and precise control of oxygen content. Faced with the dilemma of a lack of specialized equipment in the market, Zhang Yuanbo's research group embarked on a path of independent research and development of instruments.
The team completed sample cleavage and device preparation in a low-temperature environment with an inert atmosphere, and combined with microelectrode cold welding, solved the problem of single-layer copper oxide being easily damaged by air and water vapor. More importantly, the team has developed doping control technology with extremely high precision, achieving reversible regulation of oxygen content.
We measure while precisely adjusting the oxygen content of the material by controlling the ozone concentration and temperature, "said Ruan Wei, one of the corresponding authors and a professor in the Department of Physics at Fudan University. With this "in-situ control" technology, the team achieved a doping resolution of up to δ p ≈ 0.0005, allowing observation of the complete physical phase diagram from the Mott insulating phase to the entire superconducting dome.
Based on cutting-edge experimental instruments and innovative technologies, they found that the optimal superconducting transition temperature of single-layer materials is reduced by about 10% compared to bulk materials, indicating that thickness does indeed affect superconducting temperature. However, at the same time, the single-layer material fully preserves the associated system characteristics of the bulk material, indicating that although the decrease in thickness affects the superconducting transition temperature, the core physical properties of copper oxide still remain intact in a single CuO ₂ plane, which also provides a key verification of the superconducting properties at the two-dimensional limit.
By utilizing high-precision controllability of the extremely under doped region, the team further reduced the temperature to about 100 mK and explored the quantum critical region of superconductivity insulator, achieving unexpected discoveries. The team observed a peculiar quantum critical phenomenon in single-layer Bi-2201: as the temperature decreases, the universal scaling behavior near the traditional quantum critical point fails, and instead its effective critical exponent rapidly diverges as it approaches the critical region, exhibiting typical quantum Griffith singularity.
More importantly, at the zero temperature limit, an anomalous metallic state occurs between superconductivity and insulation, with a finite value of resistance saturated at low temperatures. This anomalous metallic state can be obtained by reducing hole doping or by applying a perpendicular magnetic field. This discovery is consistent with the image of Bose metal: high-temperature superconductivity emerges from a two-dimensional Bose system without gaps or superfluidity through quantum phase transitions.
This discovery not only reveals the true dimensionality effect in a single CuO ₂ surface, but also provides a highly adjustable and high-quality two-dimensional experimental platform for studying quantum critical phenomena and anomalous metal states.
Continuously contributing to the field of high-temperature superconductivity
Anchoring core issues and tackling difficulties over several years is a distinctive feature of Zhang Yuanbo's team's steady and in-depth exploration. This achievement not only pushes high-temperature superconductivity to the true single-layer limit and discovers new phenomena that have not been observed by previous researchers, but also lays a solid foundation for studying the mechanism of high-temperature superconductivity.
Our contribution can be said to have added a brick to the field. "The team stated that this research has achieved both" clean system "and" fine regulation "for the first time under the limit of single copper oxygen surface, providing an experimental platform for" controllable variables ", allowing researchers to systematically track the complete transformation path of superconductivity from scratch and from weak to strong.
High temperature superconductivity has been discovered for nearly forty years since 1986, and its mechanism has not yet been fully deciphered. However, every approach to the "limit conditions", thinner, purer, and more controllable materials, is a step forward, pushing the boundaries of the answer deeper.
Next, the team will continue to focus on major issues in the field of high-temperature superconductivity and explore higher performance high-temperature superconductors; Overcome key challenges in the preparation process and physical property measurement of materials and devices, and continuously promote research in new two-dimensional quantum materials and other directions.
Professors Zhang Yuanbo and Ruan Wei from the Department of Physics at Fudan University, as well as Professor Chen Xianhui from the University of Science and Technology of China, are the co corresponding authors of the paper. Research partners include Fudan University, University of Science and Technology of China, University of British Columbia, Zhejiang University, Renmin University of China, Shanghai Jiaotong University, Institute of Physics of the Chinese Academy of Sciences, Weizmann Institute of Science, Tsinghua University, etc. This study has received support from the National Key Research and Development Program of the Ministry of Science and Technology, the Basic and Interdisciplinary Breakthrough Program of the Ministry of Education, the Original Exploration Program of the National Natural Science Foundation of China, major projects of the Ministry of Science and Technology, the Shanghai Science and Technology Commission, the New Cornerstone Science Foundation, and other projects and units.
