Experimental Electronic Structure of Infinite-layer Nickelate Superconductor

The emerging nickelates has developed into high-Tc superconducting systems with transition temperatures exceeding the liquid-nitrogen boiling temperature. From the infinite-layer to the RP phase, nickelate superconductors span from the Mott-Hubbard regime to the charge-transfer regime, accompanied by changes in Tc and the valence state of Ni. Exploring the driving force behind these transitions and the relevant superconducting parameters will provide key clues for future research into the origin of high-Tc superconductivity. From this perspective, nickelate superconductors have become a uniquely complete system for high-Tc superconductivity research, and understanding the electronic structure of infinite-layer nickelate superconductors is an essential part of this.Although there are significant experimental challenges in revealing the electronic structure of infinite-layer films due to topochemical reduction, we will discuss the latest progress in the in-situ preparation of infinite-layer nickelate superconducting films and their angle-resolved photoemission spectroscopy (ARPES) measurements. We carefully compare our experimental results with theoretical predictions, focusing on the disappearance of the La d_z2 pocket around Gamma point, the features of heavy hole doping, and comparison to cuprates. These findings will further advance the mechanisms behind high-Tc superconductivity.