Two single crystalline samples with the same nominal composition of Rb${}_{0.8}$Fe${}_2$Se${}_2$ 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 $T_c$ 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.

• Received 16 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.184517