Infinite-layer nickelates have recently emerged as a promising platform for studying unconventional superconductivity. In particular, Sm-based nickelates exhibit the highest superconducting transition temperatures reported so far among infinite-layer nickelates, raising important questions about the microscopic ingredients responsible for the enhanced superconductivity.

To address this issue, we performed Ni L-edge resonant inelastic x-ray scattering (RIXS) measurements on superconducting Sm_1−x−yEu_xCa_yNiO₂ (SECNO) thin films. Our experiments reveal dispersive paramagnon excitations in both optimally doped and overdoped SECNO samples, demonstrating that robust spin correlations persist in these high-T_c nickelate superconductors. By comparing SECNO with Pr-based infinite-layer nickelates, we find that the enhanced T_c in Sm-based compounds is accompanied by a reduced in-plane magnetic exchange coupling, in contrast to the trend commonly observed in hole-doped cuprates. These results point to a distinct superconducting mechanism in nickelates and suggest that rare-earth electronic states and interlayer coupling may play an important role in optimizing superconductivity.

This work has been published in Nature Communications (Y. Yan, Y. Chan, A. Ariando^✉, J. Chang^✉, Q. Wang^✉ et al. Persistent paramagnons in high-temperature infinite-layer nickelate superconductors. https://doi.org/10.1038/s41467-026-73083-3). This work is in close collaboration with Prof. A. Ariando from NUS and Prof. Johan Chang from UZH. We are thankful to all collaborators.