Bulk superconductivity and disorder in single crystals of LaFePO
  We have studied the intrinsic normal and superconducting properties of the oxypnictide LaFePO. These samples exhibit bulk superconductivity and the evidence suggests that stoichiometric LaFePO is indeed superconducting, in contrast to other reports. We find that superconductivity is independent of the interplane residual resistivity $\rho_0$ and discuss the implications of this on the nature of the superconducting order parameter. Finally we find that, unlike $T_c$, other properties in single-crystal LaFePO including the resistivity and magnetoresistance, can be very sensitive to disorder. 
James G. Analytis, Jiun-Haw Chu, Ann S. Erickson, Chris Kucharczyk,   Alessandro Serafin, Antony Carrington, Catherine Cox, ...