Superconductivity around quantum critical point in P-doped iron arsenides

We demonstrate that, by the P/As substitution-without doping of charge carriers-in a FeAs-layer-based parent compound, superconductivity can be universally introduced. The maximum superconducting critical temperature (Tc) of BaFe2(As1-xPx)2 achieves 30 K. The P doping in LnFeAsO system (Ln = La and Sm) produces superconductivity below 11 K. The normal-state resistivity obeys linear temperature dependence and the normal-state Hall coefficient shows strong temperature dependence. These non-Fermi liquid behaviors suggest magnetic quantum criticality. The maximum Tc values in different systems correlates strongly with the diagonal bondangle of Fe-As-Fe, implying the important role of the next-nearest-neighbor magnetic exchange coupling in iron pnictide superconductors.