Franck-Condon blockade and giant Fano factors in transport through single molecules

TL;DR

This paper demonstrates that strong electron-vibrational coupling in single molecules causes Franck-Condon blockade, leading to suppressed current and giant Fano factors due to avalanche-like electron transport, with self-similar avalanches over multiple time scales.

Contribution

It reveals the impact of Franck-Condon physics on electron transport, highlighting the emergence of large Fano factors and avalanche phenomena in molecular conductance.

Findings

Current suppression at low bias due to Franck-Condon blockade

Giant Fano factors ($10^2$--$10^3$) observed in transport

Self-similar avalanche-like electron transport over various time scales

Abstract

We show that Franck-Condon physics leads to a significant current suppression at low bias voltages (termed 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 ($10^2$--$10^3$), 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.