Superconductivity at 2.2 K in the layered oxypnictide La3Ni4P4O2

We report the observation of superconductivity in La3Ni4P4O2 at 2.2 K. The layer stacking in this compound results in an asymmetric distribution of charge reservoir layers around the Ni2P2 planes. The estimated Wilson ratio, R-W approximate to 5, indicates the presence of strongly enhanced normal-state susceptibility, but many of the basic superconducting characteristics are conventional. The estimated electronic contribution to the specific heat, gamma approximate to 6.2 mJ mol-Ni-1 K-2, is about 2/3 of that found in layered nickel borocarbide superconductors.