The mechanism of high-temperature (TC) superconductivity is a key challenge in condensed matter physics. Recently, Chinese scientists made significant progress in the study of high-TC nickelate superconductors.
For the first time, scientists observed a nodeless superconducting gap and discovered electron-boson coupling by measuring the electronic structures of Ruddlesden-Popper bilayer nickelate superconducting thin films. These results provide crucial evidence for two fundamental issues in the mechanism of high-TC nickelates: “superconducting gap symmetry” and “superconducting pairing mechanism”.
This study, conducted by a team led by Prof. HE Junfeng from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences, in collaboration with a team led by Prof. XUE Qikun and Prof. CHEN Zhuoyu from the Southern University of Science and Technology (SUSTech), was published in Science on May 21, 2026.
Since its discovery in 1911, superconductivity, with extreme electromagnetic properties, has become an important research direction in the scientific community. In the past century, copper-based and iron-based high-TC superconductors have been discovered. However, the high-TC superconducting mechanism remains unresolved. The recent emergence of nickel-based high-TC superconductors (nickelates) has provided a new opportunity for understanding the mechanism.
In high-TC superconductors, the “superconducting gap symmetry” is recognized as a milestone for understanding the superconducting mechanism. Therefore, exploring the “superconducting gap symmetry” in nickelates is extremely important. Specifically, whether the superconducting gap has “nodes” (points where the superconducting gap is zero) in momentum space is a key for revealing the superconducting gap symmetry. The researchers have carried out measurements on Ruddlesden-Popper bilayer nickelate superconducting thin films using angle-resolved photoemission spectroscopy (ARPES). No gap node was observed in the entire momentum space, being consistent with s-wave (s±) superconducting gap symmetry.
Understanding how “electron pairs” are formed is another key issue for the mechanism of high-TC superconductivity. In principle, electrons may pair through “electron-boson coupling”. The researchers found a dispersion kink at ~70 meV below the Fermi level, which is a “finger print” of electron-boson coupling. This observation provides crucial evidence for understanding the electron pairing mechanism.
In this collaborative research, the SUSTech team led the efforts of thin film growth, and the USTC team led the measurements of the electronic structures of the thin films. To address the technical challenge of oxygen loss during sample transfer, researchers developed a new technology based on liquid-nitrogen-cooled ultra-high vacuum low-temperature sample quenching and transfer. This new technology successfully enabled the transfer of samples from Shenzhen to Hefei and ensured the success of the experiments.
