Electronic structure of superconducting nickelates probed by resonant photoemission spectroscopy

作者：Chen, Zhuoyu^*; O***a, Motoki; Li, Danfen; Been, Emily M.; Chen, Su-Di; Hashimoto, Makoto; Lu, Donghui; Mo, Sung-Kwan; Lee, Kyuho; Wang, Bai Yang; Rodolakis, Fanny; McChesney, Jessica L.; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P.; Hwang, Harold Y.; Shen, Zhi-Xun^*

来源：Matter, 2022, 5(6).

DOI：10.1016/j.matt.2022.01.020

• COPPER

The discovery of infinite-layer nickelate superconductors has spurred enormous interest. While the Ni1+ cations possess nominally the same 3d(9) configuration as Cu2+ in cuprates, the electronic structure variances remain elusive. Here, we present a soft X-ray photoemission spectroscopy study on parent and doped infinite-layer Pr-nickelate thin films with a doped perovskite reference. By identifying the Ni character with resonant photoemission and comparison with density functional theory + U (on-site Coulomb repulsion energy) calculations, we estimate U ~5 eV, smaller than the charge transfer energy delta ~8 eV, confirming the Mott-Hubbard electronic structure in contrast to charge-transfer cuprates. Near the Fermi level (EF), we observe a signature of occupied rare-earth states in the parent compound, which is consistent with a self-doping picture. Our results demonstrate a correlation between the superconducting transition temperature and the oxygen 2p hybridization near EF when comparing hole-doped nickelates and cuprates.