ESR STUDIES OF K-DOPED C60

Precise electron spin resonance (ESR) spectroscopic studies have been done for KxC60. Three ESR peaks corresponding to the three important crystal phases of KxC60 (face-centered cubic K3C60, body-centered tetragonal K4C60, and body-centered cubic K6C60) are reported. From the temperature dependencies of the ESR intensity for these three phases, it is confirmed that the superconducting K3C60 phase is metallic, and that both of the non-superconducting K4C60 and K6C60 phases are semiconducting or insulating. The electronic properties of KxC60 are discussed in comparison with those of RbxC60 and KxC70.