Charge-memory effects such as bistability and switching between a charged and a neutral state, have been recently observed in an increasing number of experiments on charge transport through molecules[1,2]. We consider a charge-memory effect in the framework of a minimal polaron model. It is shown that in the case of strong electron-vibron interaction the rate of spontaneous quantum switching between two metastable states is exponentially suppressed at zero bias voltage, while remaining large enough at finite voltage. The switching between states at finite voltage and hysteretic charge-voltage curves are calculated at weak coupling to the leads by the master equation method, and at stronger coupling to the leads by the equation-of-motion method for nonequilibrium Green functions.
[1] Jascha Repp et al, Science, vol 35, 493-495 (2004)
2] F. E. Olsson et al, PRL, vol 98, 176803 (2007)