Franck-Condon Blockade and Giant Fano Factors in Transport Through Single Molecules

We show$^1$ that Franck-Condon physics leads to a significant current suppression at low bias voltages (termed {\it Franck-Condon blockade}) in transport through single molecules with strong coupling between electronic and vibrational degrees of freedom. We find that transport in this regime is characterized by remarkably large Fano factors ($10^2$ - $10^3$ for realistic coupling parameters), which arise due to avalanche-like transport of electrons. Avalanches occur in a self-similar manner over a wide range of time scales, as reflected in power-law dependences of the current noise on frequency and vibrational relaxation rate. \\ \\ $^1$ Jens Koch and Felix von Oppen, cond-mat/0409667