High-pressure study of superconducting and non-superconducting single   crystals of the same nominal composition Rb0.8Fe2Se2
  Two single crystalline samples with the same nominal composition of Rb0.8Fe2Se2 prepared via slightly different precursor routes under the same thermal processing conditions were investigated at ambient and high pressures. One sample was found superconducting with a Tc of ~31 K without the previously reported resistivity-hump and the other was unexpectedly found to be a narrow-gap semiconductor. While the high pressure data can be understood in terms of pressure-induced variation in doping, the detailed doping effect on superconductivity is yet to be determined. 
M. Gooch (1), B. Lv (1), L. Z. Deng (1 and 2), T. Muramatsu (1), J.   Meen (1 and 3), Y. Y. Xue (1 and 2), B. Lorenz (1 and ...
cond-mat.supr-con