Ultrafast Rattling Motion Of A Single Atom In A Fullerene Cage Sensed By Terahertz Spectroscopy

We have investigated the dynamical motion of a single Ce atom encapsulated in a C(82)fullerene cage (Ce@C-82) by using terahertz (THz) spectroscopy. A Ce@C(82)molecule is placed in a sub-nm gap of metal electrodes and excited by THz radiation. Two broad peaks are observed in the THz photocurrent spectra around 5 meV and 15 meV and are attributed to the lateral and longitudinal vibrational modes of the encapsulated single Ce atom, respectively. The present results demonstrate that the THz spectroscopy using nanogap electrodes has an extremely high sensitivity that can detect the dynamical motion of a single atom.