Laser pulse induced transient currents through a single molecule

Laser pulse control of electron transfer through a single molecule attached to nano electrodes is demonstrated theoretically by concentrating on the case of weak and intermediate molecule-lead coupling. A rate equation description is used to determine the populations of the different electron-vibrational states of the molecule in its neutral or charged state. Caused by the photoinduced population of excited electronic states new transmission channels are opened which change the current through the molecular junction. The transient behavior of the current is studied if the external laser pulse excitation is switched on and off or if a pulsed excitation is applied. Pulse durations of some hundreds of fs up to 50 ps are considered. Within this computational scheme the interrelation of characteristic times of charging, discharge, vibrational relaxation, and the turn on and off of the photoexciation is demonstrated. Possible self-stabilization of an excited junction state is found. Some estimates of potential effects of plasmon excitations in the leads are also given. To have a quantity available which offers direct experimental access to the transient state of the junction the time and frequency resolved photo emission spectrum of the molecule is calculated.