Signature of Superconductivity in Pressurized Trilayer-nickelate Pr$_4$Ni$_3$O$_{10-\delta}$

The discovery of high-temperature superconductivity in La$_3$Ni$_2$O$_7$ and La$_4$Ni$_3$O$_{10}$ under pressure has drawn extensive attention. Herein, we report systematic investigations on the evolutions of structure, magnetism, and electrical resistance of Pr$_4$Ni$_3$O$_{10-\delta}$ polycrystalline samples under various pressures. Pr$_4$Ni$_3$O$_{10-\delta}$ exhibits density wave transitions on Ni and Pr sublattices at about 158 K and 4.3 K, respectively, and the density wave can be progressively suppressed by pressure. A structural transformation from the monoclinic $P2_1/a$ space group to the tetragonal $I4/mmm$ occurs at around 20 GPa. An apparent drop in resistance with evident magnetic field dependence is observed as pressure above 20 GPa, indicating the emergence of superconductivity in Pr$_4$Ni$_3$O$_{10-\delta}$ polycrystalline samples. The discovery of the signature of superconductivity in Pr$_4$Ni$_3$O$_{10-\delta}$ broadens the family of nickelate superconductors and provides a new platform for investigating the mechanisms of superconductivity in the Ruddlesden-Popper phases of nickelates.