EVOLUTION OF SUPERCONDUCTIVITY OF KXC60 UPON K-DOPING - MICROWAVE LOW-FIELD SIGNAL AND ESR STUDY

By means of low magnetic-field microwave absorption (Low-Field Signal) and conventional ESR, we have studied the evolution of superconductivity in bulk KxC60 dependent on the variation of K-doping temperature and time. The first LFS as an occurrence of superconductivity is observed in a doping time as short as t(d) = 0.5 h with a discrete Tc approximately 19 K, and the volume of the superconducting phase increases on further dopings, while Tc changes slightly. The sample in a superconducting state exhibits strong ESR absorptions, which indicates the presence of a non-superconducting metallic phase coexisting with a superconducting phase in inhomogeneously doped KxC60. These phases are closely correlated and disappear at the same time by overdoping.