Superconductivity at 32 K in single-crystalline RbxFe2-ySe2

We successfully grew the high-quality single crystal of Rb0.88Fe1.81Se2, which shows a clear superconducting transition in magnetic susceptibility and electrical resistivity. Resistivity shows the onset superconducting transition T-c at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, the large upper critical field H-c2(0) has been estimated to be as high as 180 T for the field applied within the ab plane and 59 T for the field applied along the c axis. The anisotropy H-c2(ab)(0)/H-c2(c)(0) is around 3.0, lying right between those observed in KxFe2Se2 and CsxFe2Se2.