The synthesis of new FeAs-based superconductors

We report our progress in the synthesis of new compounds and superconductors in the FeAs-based family. First, we found superconductivity in hole-doped oxy-arsenide La1-xSrxFeAsO and Pr1-xSrxFeAsO. The Hall effect confirmed the hole charge carriers. Hc2(T) is higher in the hole doped samples compared with the electron doped ones. This is attributed to the higher density of states in the hole doped side. Secondly, we present some results of the fluorine-derivative parent phases SrFeAsF, CaFeAsF and EuFeAsF which we discovered independently. By doping the system with electrons, we observed superconductivity (onset point of resistivity) at about 32 K for Sr0.6La0.4FeAsF, 52.8 K for Ca0.6Pr0.4FeAsF, and 57.4 K for Ca0.6Nd0.4FeAsF. Finally, we report the discovery of a new compound (Sr3Sc2O5)Fe2As2. We have also successfully fabricated a new superconductor (Sr4V2O6)Fe2As2 (with a critical temperature of 37.2K) which is in the stoichiometric phase.