  We report the realization of superconductivity by 5d element Ir doping in
LaFeAsO, a prototype parent compound of high-temperature iron based
superconductors. X-ray diffraction patterns indicate that the material has
formed the ZrCuSiAs-type structure with a space group P4/nmm. The systematic
evolution of the lattice constants demonstrated that the Fe ions were
successfully replaced by the Ir. Both electrical resistance and magnetization
measurements show superconductivity up to 11 K in LaFe1-xIrxAsO. The
superconducting transitions at different magnetic fields were also measured
yielding a slope of -dHc2/dT = 6.7 T / K near Tc, and the upper critical field
at zero K is found to be about 55 T. This is the first example of bulk
superconductivity induced by replacing the Fe sites with higher d-orbital
electrons in FeAs-1111 family, which should add more ingredients to the
underlying physics of the iron-based superconductors.

Superconductivity