The Unusual Superconducting State at 49 K in Electron-Doped CaFe2As2 at   Ambient
  We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at ~ 49 K, which has a low critical field ~ 4 Oe, and the other at ~ 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase detected will be discussed. 
B. Lv (1), L. Z. Deng (1 and 2), M. Gooch (1), F. Y. Wei (1 and 2), Y.   Y. Sun (1), J. Meen (1 and 3), Y. Y. Xue (1 and 2),...
cond-mat.supr-con