Conduction-electron spin resonance in the superconductor K3C60

The conduction-electron spin resonance of the superconducting fulleride compound, K3C60 (T-c = 19 K) has been observed between 2.5 and 800 K at several frequencies from 9 to 225 GHz. Between T-c and 0.7T(c) the spin lifetime of normal excitations increases as predicted by the theory of Yafet for scattering from nonmagnetic structural defects. At lower temperatures the CESR arises from states bound to vortices; here the spectrum is inhomogeneously broadened and an anomalous g shift is found. The anomalous temperature dependence of the g factor and linewidth in the normal state reported by Petit et al. is most important between 50 and 250 K, suggesting that these are related to the rotation of C-60 ions.