Superconductivity at 32 K in single-crystalline Rb x Fe 2 − y Se 2

We successfully grew the high-quality single crystal of Rb${}_{0.88}$Fe${}_{1.81}$Se${}_{2}$, which shows a clear superconducting transition in magnetic susceptibility and electrical resistivity. Resistivity shows the onset superconducting transition ${T}_{\mathrm{c}}$ at 32.1 K and zero resistivity at 30 K. From the low-temperature iso-magnetic-field magnetoresistance, the large upper critical field ${H}_{\mathrm{c}2}$(0) has been estimated to be as high as 180 T for the field applied within the $\mathit{ab}$ plane and 59 T for the field applied along the $c$ axis. The anisotropy ${H}_{\mathrm{c}2}^{\mathit{ab}}$(0)/${H}_{\mathrm{c}2}^{c}$(0) is around 3.0, lying right between those observed in ${\mathrm{K}}_{x}$Fe${}_{2}$Se${}_{2}$ and Cs${}_{x}$Fe${}_{2}$Se${}_{2}$.