  The recently discovered quaternary arsenide oxide superconductor
La[O1-xFx]FeAs with the superconducting critical transition temperature (Tc) of
26 K [1], has been quickly expanded to another high-Tc superconducting system
beyond copper oxides by the replacement of La with other rare earth elements,
such as Sm, Ce, and Pr etc. [2-4], and the Pr[O1-xFx]FeAs has become to be the
first non-cuprate superconductor that holding a Tc above 50 K. All these
arsenide (including phosphide) superconductors formed in a same tetragonal
layered structure with the space group P4/nmm which has an alternant stacked
Fe-As layer and RO (R = rare earth metals) layer. Here we report the discovery
of another superconductor in this system, the neodymium-arsenide Nd[O1-xFx]FeAs
with an resistivity onset Tc of 51.9 K, which is the second non-cuprate
compound that superconducts above 50 K.
