  Nickelate superconductors have attracted a great deal of attention over the
past few decades due to their similar crystal and electronic structures with
high-temperature cuprate superconductors. Here, we report the superconductivity
in a pressurized Ruddlesden-Popper phase single crystal, La4Ni3O10 (n = 3), and
its interplay with the density wave order in the phase diagram. With increasing
pressure, the density wave order as indicated by the anomaly in the resistivity
is progressively suppressed, followed by the emergence of the superconductivity
around 25 K. Our angle-resolved photoemission spectroscopy measurements reveal
that the electronic structure of La4Ni3O10 is very similar to that of La3Ni2O7,
suggesting unified electronic properties of nickelates in Ruddlesden-Popper
phases. Moreover, theoretical analysis unveils that antiferromagnetic (AFM)
super-exchange interactions can serve as the effective pairing interaction for
the emergence of superconductivity (SC) in pressurized La4Ni3O10. Our research
provides a new platform for the investigation of the unconventional
superconductivity mechanism in Ruddlesden-Popper trilayer perovskite
nickelates.
