Terahertz dynamics of electron–vibron coupling in single molecules with tunable electrostatic potential

Clarifying electronic and vibronic properties at the individual molecule level provides key insights for future chemistry, nanoelectronics and quantum information technologies. However, information obtained by conventional single-molecule transport measurements is based on time-averaged properties. Here, we report on terahertz (THz) spectroscopy of single fullerene molecules by using a single-molecule transistor geometry. From the time-domain THz autocorrelation measurements, we obtained THz spectra associated with the THz-induced centre-of-mass oscillation of the molecules. The observed spectra reflect the potential profile experienced by the molecule on the metal surface when the number of electrons on the molecule fluctuates by one during the single-electron tunnelling process. Such an ultra-high sensitivity to the electronic/vibronic structures of a single molecule on the addition/removal of a single electron has been achieved as a result of using THz spectroscopy in the single-molecule transistor geometry. This scheme provides an opportunity to investigate the ultrafast THz dynamics of subnanometre-scale systems. Terahertz (THz) spectroscopy based on a single-molecule transistor detects a THz-induced centre-of-mass oscillation of a fullerene molecule. Its sensitivity is so high that the spectrum changes on adding (removing) an electron to (from) the molecule.