We have investigated Au atomic contacts in H$_{ 2}$ and D$_{ 2}$ environment by conductance measurement and $dI/dV$ spectroscopy. A single H$_{ 2}$ or D$_{ 2}$ molecule was found to bridge Au electrodes. In the case of the Au/H$_{ 2}$/Au junction, symmetric peaks were observed in $dI/dV$ spectra, while they were not observed for the Au/D$_{ 2}$/Au junction. The shape of the peaks in $dI/dV$ spectra originated from the structural change of the single molecule junction induced by the phonon excitation. The structural change could occur only for the Au/H$_{ 2}$/Au junction. The difference in the two single molecule junctions could be explained by larger zero point energy of Au-H$_{ 2}$ vibration mode than that in the Au/H$_{ 2}$/Au junction.
Categories: cond-mat.mtrl-sci