Abrupt Change in Dark Conductivity on C60 Polycrystalline Films at the Rotational Order/Disorder Transition

Abstract

The temperature dependence of dark conductivity of C60 fullerites in the form of polycrystalline films sandwiched between metal electrodes is systematically studied. At the rotational order/disorder phase transition temperature Tc of about 256 K, an abrupt change in dark conductivity of 4–5 orders of magnitude within a narrow temperature range of less than 2 K is observed. The conductivity for this sample decreases as the temperature crosses Tc from fcc phase to sc phase. From the Arrhenius plot of dark conductivity, the activation energies are estimated to be 53±4 meV for the fcc phase and 111±6 meV for the sc phase. To explain these experimental findings, the electric transport through parallel, extremely pure, and homogeneous C60 monocrystals between two metal contacts is postulated and described, and a model based on the local lattice potential induced by rotational order of C60 molecules is proposed.