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${}_2$.

• Received 26 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.060512