Superconductivity at 28 K in RbxC60

Meissner-effect and microwave-absorption measurements on bulk samples show that RbxC60 is superconducting with a maximum transition temperature of 28 K. This is a 10-K (60%) increase over the K-doped material. Only Ba0.6K0.4BiO3 and the cuprate superconductors have higher transition temperatures.