Dynamics of vibrational excitation in theC60single-molecule transistor

Abstract

We investigate the vibrational excitations recently observed in the single C60 molecule transistor [Park et al., Nature (London) 47, 57 (2000)]. There can be two mechanisms for this: (a) the displacement of the equilibrium position, as the electron hops onto C60 to form C 60 and (b) the position dependence of the hopping matrix element. We find that if the two electrodes are planar with the C60 sitting symmetrically between the two, then mechanism (a) is not possible, though (b) is, but the results are not in agreement with experiments. Considering C60 to be trapped between a protrusion and a flat electrode, both the mechanisms contribute and the contribution from the second can be large. For example, in the case of C60 trapped between the a protrusion and a flat electrode, the contribution can be as large as 20%. Though our results do qualitatively explain the results, for quantitative agreement with experiments, it seems necessary to consider perhaps the nonuniformity of the charge distribution in C 60 caused by the image interaction or more complex electrode geometries.