  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.
