Nickel-based superconductors have attracted great attention due to their electronic configuration, which is similar to that of copper-based high-temperature superconductors. Recently, the discovery of superconductivity with a transition temperature as high as 80 K in the bilayer nickelate La3Ni2O7 under pressure has not only reignited research interest in nickel-based superconductors but also opened new avenues for the study of unconventional superconductivity. Layered nickel-based superconductors share similar crystal structure, superconducting properties, and electronic structures with copper- and iron-based superconductors, yet they also exhibit significant differences. A deeper investigation into the electronic structure of nickel-based superconductors is expected to reveal the mechanisms behind these similarities and differences, which will further provide critical insights for a unified theoretical model and advance the understanding of unconventional superconductivity. Moreover, studies of nonequilibrium ultrafast dynamics offer new perspectives and regulations for unconventional superconductivity, which has become a vital tool. This paper focuses on the electronic structure and ultrafast dynamics of Ruddlesden-Popper phase layered nickel-based superconductors, systematically reviewing the successful applications of angle-resolved photoemission spectroscopy (ARPES) and ultrafast optical spectroscopy in nickel-based superconductivity research. Specifically, we compare the novel properties of different nickelates, including the strong electron correlation, Hund’s coupling, non-Fermi liquid behaviors, formation of energy gaps, and ultrafast electron dynamics. These advancements provide crucial experimental insights for understanding the mechanisms of unconventional superconductivity and the properties of their normal states.
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