EN
Since the discovery of high temperature superconductivity
in iron pnictides in 2008, many iron-based
superconductors (IBSs) with various crystal structures
have been exploited.Among them, superconductivity with
the onset transition temperature Tc up to 49 K has been
detected in rare earth element doped CaFe2As2 system
(CaRE122). The electron doping induced high Tc values
clearly exceed the highest Tcs induced by both hole doping
(~ 38 K) and chemical or physical pressure (~ 33 K)
in the 122-type iron-based superconductors. The occurrence
of high-Tc superconductivity in this unique system
is quite strange in terms of the much lower Tc observed
in the sister compounds bearing structural and chemical
similarities. Though the high–Tc superconductivity in
Ca1−xRExFe2As2 is of the non-bulk feature, its superconducting
origin served as a most important question has attracted
tremendous attentions ever since its discovery. In
this review, we summarize the previous experimental results
observed in this series of superconductors and list the
possible key points that may be related to the understanding
of the nature for the strange high-Tc superconductivity.