Researchers from the University of Science and Technology of China and Southern University of Science and Technology have, for the first time, observed a nodeless superconducting gap and discovered electron-boson coupling in a nickel-based high-temperature superconducting thin film. This represents a key breakthrough in the study of high-temperature superconductivity mechanisms. The related findings were published online on May 22 in the international academic journal *Science*.

The paper's corresponding authors are Academician Xue Qikun, Professor He Junfeng from the University of Science and Technology of China, and Associate Professor Chen Zhuoyu from Southern University of Science and Technology.

This discovery provides crucial experimental evidence for two central questions in high-temperature superconductivity: "superconducting gap symmetry" and "the superconducting pairing mechanism." In superconductors, electrons form pairs and move together. However, why electrons pair up and the nature of this pairing remain among the greatest mysteries in physics. To solve this puzzle, scientists have focused on two key questions.

The first question is: In what form do electrons pair? In superconductors, electron pairing allows energy savings. This saved energy is the superconducting "gap." One can imagine electron pairing as a dance duet, where the symmetry of the gap is their "dance posture." In conventional superconductors, electrons perform a "waltz" (s-wave symmetry), where the gap is non-zero everywhere. In copper-based high-temperature superconductors, electrons perform a "tango" (d-wave symmetry), where the gap becomes zero in specific directions—imagine the electrons "letting go" in these directions. Physicists refer to these gap zeros as "nodes." This study provides a clear answer for the first time in RP bilayer nickel-based high-temperature superconducting thin films: its superconducting gap has no nodes, meaning the electrons dance more like a "waltz." This suggests that nickel-based and copper-based superconductors do not share an identical pairing mechanism.

The second question is: Is there a "mediator" facilitating electron pairing? Electrons, all carrying negative charge, should naturally repel each other. The research team captured a key spectroscopic signal in their experiments—a "band kink." This is akin to a distinct bend appearing on an otherwise smooth electron energy curve. This bend at a specific location is the "fingerprint" of coupling interaction between electrons and a type of boson. This confirms the existence of electron-boson coupling in nickel-based high-temperature superconductivity, strongly suggesting that its electron pairing is likely mediated by a "mediator."

The researchers stated that this breakthrough lays a critical experimental foundation for a deeper understanding of high-temperature superconductivity mechanisms and is expected to promote the widespread application of superconducting technology.