On February 18, a joint research team led by Xue Qikun, an academician of the Chinese Academy of Sciences, from the Southern University of Science and Technology (SUST), the Guangdong-Hong Kong-Macao Greater Bay Area Quantum Science Center, and Tsinghua University published their latest research in Nature. They achieved high-temperature superconductivity of nickel oxide materials under normal pressure, with the superconducting onset transition temperature exceeding 40 Kelvin (K) - equivalent to minus 233 degrees Celsius, and observed the dual characteristics of "zero resistance" and "anti-magnetism".
This discovery makes nickel-based materials the third high-temperature superconducting material system after copper-based and iron-based materials to break the "McMillan limit" of 40K under normal pressure, providing a new breakthrough in solving the scientific problems of the mechanism of high-temperature superconductivity.
Xue Qikun (second from left) and his team members. Photo courtesy of SUSTC
Building with atomic building blocks at the nanoscale
Superconductivity is like a "zero-energy sports car" on an electric highway, with no loss when current passes through it, and is widely regarded as a disruptive technological prospect. Since the discovery of superconductivity in 1911, the search for higher-temperature superconducting materials has become an important research direction in the international scientific community.
The highest superconducting transition temperature of traditional superconductors is 40K, which is the "McMillan limit". Previously, the superconducting transition temperatures of copper-based and iron-based materials exceeded the "McMillan limit" and were called high-temperature superconductors.
In recent years, nickel-based superconducting materials have emerged. In 2019, American scientists observed superconductivity in nickel-based films for the first time, but the superconducting temperature was relatively low. In 2023, Chinese scientists achieved superconductivity in the liquid nitrogen temperature zone of nickel-based materials under a high-pressure environment of more than 100,000 atmospheres, which had a wide impact internationally. However, how to get rid of the high-pressure limitation and achieve normal-pressure high-temperature superconductivity is still an important goal pursued by scientists around the world.
In response to this challenge, since 2022, South China University of Technology President Xue Qikun and South China University of Technology Associate Professor Chen Zhuoyu of the Department of Physics have led a research team to independently develop the "strong oxidation atomic layer-by-layer epitaxy" technology.
"This technology can achieve layer-by-layer growth of atoms and precisely control the chemical ratio even when the oxidation ability is tens of thousands times stronger than traditional methods. This is like 'building atomic building blocks' at the nanoscale to construct an oxide film with complex structure, thermodynamic metastable, but perfect crystal quality," Chen Zhuoyu introduced.
The research team further applied this technology to the development of nickel-based superconducting materials, constructing an ultra-thin film only a few nanometers thick. In an extremely strong oxidizing environment, they achieved "atomic riveting", fixing the atomic structure that originally required an extremely high pressure environment to exist stably.
"During this process, we tested more than 1,000 samples and finally successfully obtained superconductivity under normal pressure. Through precise electromagnetic transport measurements, we observed zero resistance and diamagnetism, confirming the existence of high-temperature superconductivity." Chen Zhuoyu said that this breakthrough shows that by optimizing material design through interface engineering, it is expected to achieve nickel-based superconductivity at higher temperatures such as liquid nitrogen temperature.
Xue Qikun said that this is a major leap forward in the epitaxial growth technology of oxide thin films. It not only provides a solution to the oxygen deficiency problem of various oxides including wide bandgap semiconductors, but also greatly expands the artificial design and preparation of strongly correlated electronic systems such as high-temperature superconductors.
Independently developed domestic instruments
In previous high-temperature superconducting experimental research, the equipment used was mainly imported. This situation has largely restricted the autonomy and innovation of my country's high-temperature superconducting research.
In addition, high-temperature superconducting experiments have extremely stringent requirements for ultra-high vacuum, ultra-strong oxidation environment, atomic-level deposition accuracy, and high automation, forcing the research team to rely on imported equipment when conducting research.
The research team has joined forces with a number of domestic equipment manufacturers to form a joint technical group consisting of material scientists, precision mechanical engineers and automation control experts. They have developed the world's first thin-film epitaxial equipment that combines super-strong oxidation atmosphere with atomic-level deposition accuracy, achieving an oxidation efficiency that is tens of thousands times higher than similar international equipment.
"Compared with foreign countries, China's industrial ecology has great advantages. Multiple equipment manufacturers can cooperate well, and many complex needs can be met." Chen Zhuoyu said. In this process, the research team explored a new school-enterprise collaborative R&D paradigm of 'scientific research traction-joint development-iterative upgrade'.
By sending technical personnel to establish long-term cooperative relationships with university laboratories, local enterprises can grasp the operating status of equipment in real time and quickly complete repairs or provide alternative solutions when failures occur, thus supporting scientific research work to the greatest extent possible. This not only improves the efficiency of equipment use, but also promotes the continuous iteration and upgrading of equipment to achieve a higher level of operation.
The average age is 28 years old, and young forces are constantly emerging
Chen Zhuoyu, 35, is the main contributor to this research. In 2022, after completing his postdoctoral research at Stanford University in the United States, he returned to his hometown of Shenzhen and joined SUSTech.
Under the leadership of Xue Qikun, Chen Zhuoyu set up a superconducting mechanism laboratory from scratch and carried out high-temperature superconductivity research. In just three years, he formed a research team mainly composed of postdoctoral fellows and graduate students. The average age of team members was only 28 years old.
Nickel-based superconductors are a hot topic in the international scientific community, and global competition is extremely fierce. In the process of tackling this problem, the Stanford University research team and its collaborators almost simultaneously reported normal-pressure superconductivity in a similar material system. The Chinese and American teams have independent research paths, and their experiments confirm each other.
"Due to the fierce international competition, we organized several teams to take turns to do experiments, follow up the experimental results, give feedback, make plans every day, and write articles immediately after discovering superconducting signals." Chen Zhuoyu said that the research has attracted great attention from the academic community after it was published. The reviewer commented that this work is an important breakthrough in nickel-based superconductor research.
"This achievement has achieved a superconducting temperature of nickel oxide above 40K under normal pressure, which will promote deeper and more extensive research on nickel-based superconductors, and is expected to promote research on the common mechanisms of three types of high-temperature superconducting systems: copper-based, iron-based, and nickel-based. In addition, this achievement stems from long-term accumulated technological breakthroughs and is an innovation in the application of strong oxidation and material systems, providing new ideas for the research of high-temperature superconducting materials." Chen Xianhui, an academician of the Chinese Academy of Sciences, commented.
(Related paper information: https://doi.org/10.1038/s41586-025-08755-z, original title: "Breaking the Limit! my country has achieved important results in the field of high-temperature superconductors")
