The newly discovered superconductivity in the infinite-layer nickelates has become a subject of intense interest. It has been shown that the superconducting transition temperature T_c can be increased by 40% for Pr_0.8Sr_0.2NiO₂, when the substrate changes from SrTiO₃ (STO) to (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (LSAT), which applies compressive strain to the film. To understand the underlying mechanism, we performed resonant inelastic x-ray scattering (RIXS) studies on the undoped PrNiO₂ films grown on the two different substrates and investigated the strain effect on the magnetic excitations. Our experiments show that the strain-tuning has marginal influence on the magnon bandwidth, in sharp contrast to the enhancement of T_c in the doped films. Since magnetism is one of the candidates to mediate Cooper pairs, this finding provides important implications for elucidating the superconductivity mechanism in infinite-layer nickelates.

This work has been recently published in Nature Communications (Gao, Q., Fan, S. Wang, Q. et al. Magnetic excitations in strained infinite-layer nickelate PrNiO₂ films. https://doi.org/10.1038/s41467-024-49940-4). We are thankful to collaborators from NSLSII-BNL, LQMR-UZH, Diamond Light Source, MIT, Clemson University, Canadian Light Source, and especially Prof. Zhihai Zhu’s team at IOP-CAS who has spearheaded this project.