Chinese scientists have achieved another landmark advance in the research of nickel-based high-temperature superconductors. A research team led by Xue Qikun and Chen Zhuoyu from the Shenzhen Institute of Quantum Science and Engineering, the Department of Physics, and the National Key Laboratory of Quantum Functional Materials at Southern University of Science and Technology, in collaboration with the team led by Shen Dawei from the University of Science and Technology of China, recently published their latest findings in the prestigious international journal Nature. Under extreme oxidizing conditions, the team has successfully created two brand-new nickel-based high-temperature superconducting materials at ambient pressure through artificially designed atomic stacking sequences.
Using angle-resolved photoemission spectroscopy (ARPES), the researchers have also identified the key electronic band structure closely associated with the superconducting state, providing crucial experimental evidence for unraveling the mechanism of nickel-based high-temperature superconductivity.
Like building with Lego blocks: New superconductors are designed and constructed at the atomic level
Superconductivity refers to a phenomenon in which materials exhibit zero electrical resistance and allow lossless electric current flow under specific conditions. Research on high-temperature superconductivity stands as one of the most cutting-edge topics in condensed matter physics. Following copper-based and iron-based high-temperature superconductors, nickel-based materials are regarded as the third important system expected to help scientists further understand the mechanism of high-temperature superconductivity. In-depth investigations into this system are not only relevant to the frontiers of basic science but are also expected to inspire vital advances in future energy transmission, precision detection, information technology, quantum computing, and other fields.
Nevertheless, research on nickel-based superconducting materials has long been plagued by a core challenge: the highly oxidized state required for superconductivity conflicts sharply with the conditions needed for stable material growth. This is comparable to simultaneously firing the body and glaze of a porcelain piece – the formation of the porcelain body demands a mild and stable environment, while glaze coloring requires fierce fire and strong oxygen. The contradictory conditions make it extremely difficult to satisfy both requirements using traditional methods.
To tackle this dilemma, the research team independently developed a technique called “strong-oxidation atomic layer-by-layer epitaxy”. This technique enables atomic-precision control of the material growth process in an ultra-strong oxidizing environment, allowing the thin film to complete structural assembly and full oxidation simultaneously during deposition. Much like stacking “atomic Legos” in the nanoworld, scientists can precisely arrange atoms such as lanthanum, praseodymium, and nickel according to a pre-designed blueprint, thereby fabricating a series of high-quality nickel-based oxide thin films. According to the researchers, this capability to achieve atomic-level engineering under extreme oxidizing conditions not only provides a unique experimental platform for nickel-based superconductivity research but also offers a new solution to the oxygen-deficiency challenges plaguing various oxide materials.
Leveraging this technology, the team first raised the onset superconducting transition temperature of the previously discovered pure double-layer nickel-based thin film from 45 Kelvin to 63 Kelvin at ambient pressure. Following this, they precisely synthesized three brand-new nickel-based superstructure materials following artificially designed atomic stacking schemes. Two of these materials exhibit high-temperature superconductivity at ambient pressure, with onset transition temperatures reaching 50 Kelvin and 46 Kelvin, respectively. This means the research team has not only improved the performance of known materials but also created novel superconducting materials that do not exist naturally.
Mapping the energy-momentum structure of superconducting electrons: A key to unlocking the mystery of high-temperature superconductivity
Discovering new materials is only the first step; understanding why superconductivity occurs is the more fundamental scientific question. To this end, the team combined atomic-precision structural control with angle-resolved photoemission spectroscopy to conduct a systematic comparative study of four nickel-based oxide thin films with different stacking structures.
Angle-resolved photoemission spectroscopy can directly observe the energy and momentum distribution of electrons in materials, and is vividly described as a “super camera” that takes “photos” of electron motion. The study found that a Fermi pocket formed by the γ band exists near the corner of the Brillouin zone in all superconducting structures, whereas this critical feature is absent in non-superconducting structures.
This finding experimentally reveals the correlation among atomic stacking configuration, electronic band structure, and superconductivity, and identifies the “electronic genes” that determine the occurrence of superconductivity, providing clear experimental evidence for uncovering the microscopic mechanism of nickel-based high-temperature superconductivity.
The researchers note that nickel-based, copper-based, and iron-based families of high-temperature superconductors feature distinct electronic structures. A systematic comparative study of these three systems will help humanity ultimately solve the major scientific puzzle of high-temperature superconductivity and lay a scientific foundation for the development of future technologies in energy, information, quantum computing, and beyond.