NONLINEAR LOGARITHMIC TIME DECAY OF MAGNETIZATION IN SUPERCONDUCTING RB3C60

We have measured the time decay of the magnetization for a well charac terized superconducting fullerene Rb3C60. The temperature dependence o f the magnetic relaxation rate dM(t)/dln(t) exhibits a maximum at a ch aracteristic temperature T(max), which decreases with increasing field . At low temperatures a nonlinear logarithmic time decay of the magnet ization is observable only after several hours, but is clearly observa ble after much shorter times at high temperatures. This nonlinear beha vior suggests the existence of a vortex glass state in Rb3C60 and is c onsistent with the collective creep model.