Abstract:
In this presentation, I report systematic investigation of various doping approaches and the effects on superconductivity in the recently-discovered FeAs-based superconductors. Main three type doping approaches are presented as below. (1) Superconductivity induced by Th doping in Ln-1111 system and a record of Tc=56 K is reached in Gd1-xThxFeAsO system. (2) Superconductivity induced by doping of Co or Ni on Fe site in both 1111 and 122 systems. A dome –like doping dependence of Tc is observed. The result points to an itinerant picture of 3d electrons in the iron arsenides. We also observed that the absolute value of thermopower is enhanced at the optimal doping level, suggesting a correlation between Tc and thermopower. The doping effect of non-magnetic impurity Zn is investigated and a possible change in the pairing symmetry with doping level is proposed. (3) Chemical pressure is induced by doping of P on As site and superconductivity is observed. In P-doped Eu-122, a coexistence of superconductivity and ferromagnetism is observed. In P-doped Ba-122 system, a possible quantum critical point of Fe SDW is evidenced. A rich phase diagram of CeFeAs1-xPxO system is revealed and we suggested that the inter-layer Kondo coupling plays an important role in the rare earth iron pnictides.
Coffee and tea will be served 20 minutes prior to the seminar.