Time-dependent electron transport through molecular quantum dots in the presence of external irradiation

We present a fully nonequilibrium calculation of the low-temperature transport properties of a single molecular quantum dot coupled to the local phonon mode when an ac field is applied to the gate. The resonant behaviour is shown in the time-averaged differential conductance as the ac frequency matches the frequency of the local phonon mode, which is a direct consequence of the satellite-phonon-peak structure in the dot electron spectral function. Different step structure with and without the external irradiation is found in the I-V curves, and oscillation behaviour is found in the step height as a function of the irradiation intensity.