Superconductivity at 8 K in samarium-dopedC60

We have synthesized the fulleride system ${\mathrm{Sm}}_{\mathit{x}}$ ${\mathrm{C}}_{60}$ (x<3). It is found that Sm can be intercalated into interstitial sites of ${\mathrm{C}}_{60}$ to form a solid solution. For the nominal composition x=3, the sample shows superconductivity at ${\mathit{T}}_{\mathit{c}}$=8 K. X-ray diffraction reveals an orthorhombic structure with a=28.17(5) Å, b=28.07(3) Å, and c=28.27(3) Å, derived from the face-centered cubic cell of ${\mathit{A}}_3$ ${\mathrm{C}}_{60}$ by doubling in each direction and analogous to that of ${\mathrm{Yb}}_{2.75}$ ${\mathrm{C}}_{60}$. The lattice parameters of Sm-doped ${\mathrm{C}}_{60}$ are significantly larger than those of Yb-doped ${\mathrm{C}}_{60}$ and the superconducting transition temperature of ${\mathrm{Sm}}_3$ ${\mathrm{C}}_{60}$ is 2 K higher than that of ${\mathrm{Yb}}_{2.75}$ ${\mathrm{C}}_{60}$.