Controlled Contact to a C60 Molecule

The conductance of C60 on Cu(100) is investigated with a low-temperature scanning tunneling microscope. At the transition from tunneling to the contact regime the conductance of C60 adsorbed with a pentagon-hexagon bond rises rapidly to 0.25 conductance quanta G0. An abrupt conductance jump to G0 is observed upon further decreasing the distance between the instrument's tip and the surface. Ab-initio calculations within density functional theory and non-equilibrium Green's function techniques explain the experimental data in terms of the conductance of an essentially undeformed C60. From a detailed analysis of the crossover from tunneling to contact we conclude that the conductance in this region is strongly affected by structural fluctuations which modulate the tip-molecule distance.