Charge pumping in strongly coupled molecular quantum dots

Abstract

The interaction between electrons and the vibrational degrees of freedom of a molecular quantum dot can lead to an exponential suppression of the conductance, an effect which is commonly termed Franck-Condon blockade. Here, we investigate this effect in a quantum dot driven by time-periodic gate voltages and tunneling amplitudes using nonequilibrium Green's functions and a Floquet expansion. Building on previous results showing that driving can lift the Franck-Condon blockade, we investigate driving protocols which can be used to pump charge across the quantum dot. In particular, we show that due to the strongly coupled nature of the system, the pump current at resonance is an exponential function of the drive strength.

Full counting statistics for electron transport in periodically driven quantum dots

“…The system's periodicity within time allows for objects of interest to be cast as Fourier series [6,33,78]. For a given twotime object, the Fourier coefficients are calculated as…”

“…The dynamical response of a junction to the modulation of a voltage or to the irradiation by a light source offers intriguing means of probing and controlling the system's dynamics [1]. Applications include optically irradiated nanoscale junctions [2,3], electron pumping [4][5][6], pump-probe spectroscopy [7,8], and AC current rectification [9,10]. The exploration of time-dependent phenomena has a long history [1,11], which mostly centers on periodic drivings, typically induced with microwave radiation.…”

“…The need for a counting field complicates derivations within a time-dependent setting, as the equations of motion for the Green's functions become unwieldy integro-differential equations within the Keldysh-Schwinger space. In this paper, using Floquet Green's functions [6,33,77,78], we investigate full counting statistics for modeling systems with periodic driving of the leads. The periodicity within the system's dynamics allows for the Green's functions of the system to be cast as Fourier series.…”

Nonadiabatic particle and energy pump at strong system-reservoir coupling

“…In the nonadiabatic regime, we find values of the parameters wherein the output energy is maximum and accompanied by a coefficient of performance that is close to the maximum value too. Moreover, the device that we are proposing is feasible with current technology [16][17][18]20 and hence, our results can be scrutinized experimentally.…”

“…Phononics 1 , the study of the flow of energy carried by phonons in quantum systems, has led to the idea of quantum heat pumps that can transport energy even against a temperature bias 2 . In electronic transport, an analogous device called an electron pump, which can be a junction that uses gate potentials to propagate electrons without the action of a source-drain bias, has been studied extensively in both the adiabatic [3][4][5][6][7][8][9][10] and the nonadiabatic [11][12][13][14][15][16][17][18][19][20] regimes. The pumping of energy carried by electrons has also been studied either in the weak system-environment coupling regime 21 or in the adiabatic regime 22,23 , with the exception of specialized coherent transport models that have been studied in the non-adiabatic regime 24 .…”