In laboratories in Hefei and Shenzhen, Chinese physicists have cracked open a door that's been sealed for over a century: they've observed a nodeless superconducting gap in nickelate films, revealing a fundamental truth about how high-temperature superconductors work. The discovery, published in Science by teams led by Prof. He Junfeng at the University of Science and Technology of China and Profs. Xue Qikun and Chen Zhuoyu at the Southern University of Science and Technology, tackles one of condensed matter physics' most stubborn puzzles—a question that has consumed the field ever since superconductivity was first discovered in 1911.
For decades, scientists have chased the mechanism behind high-temperature superconductivity, the strange phenomenon where certain materials lose all electrical resistance below a critical temperature. Copper-based and iron-based superconductors were discovered in the twentieth century, but their workings remained mysterious. When nickel-based superconductors—nickelates—emerged recently, they offered a fresh angle on the old mystery. Understanding these materials could unlock not just academic knowledge, but potentially transformative technologies: perfectly efficient power transmission, frictionless transportation, and computing systems unlike anything we have today.
The key to understanding any superconductor lies in two fundamental questions: What is the shape of the superconducting gap—the energy difference between superconducting and normal states? And how do electrons pair up to create superconductivity in the first place? The team focused on Ruddlesden-Popper bilayer nickelate thin films, using a technique called angle-resolved photoemission spectroscopy (ARPES) to map the electronic structure with extraordinary precision. When they scanned the entire momentum space, they found something crucial: no gap nodes—no points where the gap dropped to zero. This observation aligns with s-wave superconducting gap symmetry, a pattern long theorized but now confirmed in nickelates for the first time.
The second breakthrough came from detecting electron-boson coupling, the mechanism by which electrons pair together. The researchers found a distinct "fingerprint" at approximately 70 meV below the Fermi level—a dispersion kink that reveals how electrons interact with boson excitations to form the pairs that enable superconductivity. It's the smoking gun evidence researchers have long sought.
What makes this achievement even more remarkable is the technical ingenuity behind it. Transferring delicate superconducting samples between cities without degrading them presented an extraordinary challenge, since oxygen loss during transport could destroy the very properties the team wanted to measure. The researchers developed an innovative solution: a liquid-nitrogen-cooled ultra-high vacuum low-temperature sample quenching and transfer system that successfully preserved samples as they traveled from Shenzhen to Hefei. This methodological breakthrough may prove as valuable as the scientific results themselves, opening doors for future collaborative research on fragile quantum materials.
The findings narrow the gap between theory and experiment, bringing the field closer to a unified understanding of high-temperature superconductivity. In doing so, they inch humanity toward technologies that seemed impossible just years ago.