High-pressure study of superconducting and nonsuperconducting single crystals of the same nominal composition Rb_0.8Fe₂Se ₂

Two single crystalline samples with the same nominal composition of Rb _0.8Fe₂Se₂ 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 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.