Low-frequency elastic response in single-crystal C60

The complex elastic constant of sublimation grown C60 single crystals is measured between 100K and 300K in the frequency range 0.6 Hz - 50 Hz. The order disorder phase transition at TI = 260K shows up in a negative dipanomaly and a peak maximum in the real and imaginary parts of the complex elastic constant, respectively. A very slow relaxation (τ = 0.2s) was measured near TI. In addition the elastic behaviour around the frequency dependent freezing transition at TII is measured and described by a single activated relaxation time τ. From our data and the data of previous measurements we find, that the frequency shift of TII from 180 K to 80 K can be described by a simple Arrhenius behaviour over a frequency range of 11 decades. (orig.)