Since the discovery of superconductivity in infinite-layer nickelates in 2019, the subsequent discovery of high-temperature superconductivity at 80 K in La3Ni2O7 under high pressure has established nickelates as a new family of high-Tc superconductors, alongside cuprates and iron-based systems. This breakthrough has since been extended to other Ruddlesden–Popper (RP) nickelates under pressure, as well as to thin-film forms at ambient pressure.

Over the past several years, researchers worldwide have devoted extensive efforts to unraveling the fundamental properties and superconducting mechanism of nickelates. A complex landscape has emerged, featuring density-wave-like orders, structural transitions, strange-metal behavior, and orbital-dependent electronic correlations, alongside critical roles played by oxygen vacancies, magnetic excitations, and doping in shaping the phase diagram. Notably, superconductivity has also been realized in thin films of RP nickelates at ambient pressure.

In this talk, we review these key experimental discoveries and discuss the essential parameters that govern the emergence of high-Tc superconductivity in RP nickelates, providing insights into the mechanism of unconventional superconductivity.