Low frequency elastic properties of the structural and freezing transitions in single-crystalC60

We present the first low frequency (0.1–50 Hz) measurements of the complex elastic constant on ${\mathrm{C}}_{60}$ single crystals. We have measured a negative dip anomaly of 25% at ${\mathit{T}}_{\mathrm{I}}$=261 K, which did not show up in previous elastic studies at ${10}^4$ Hz. The slow relaxation observed near ${\mathit{T}}_{\mathrm{I}}$ is supposed to be due to the very slow dynamics of the order parameter fluctuations. In addition it is shown that the elastic anomalies observed at ${10}^4$ Hz and 160 K originate from the same physical process as the ‘‘glass’’ transition at 80 K observed in thermal expansivity.