Electron transport properties of molecular junctions with anharmonic double-well potentials

Abstract

In the present paper, we investigated the electron transport properties of molecular junctions with anharmonic vibrations described by double-well potentials in the sequential tunneling regime. It was found that the suppression of the low-bias current caused by strong electron-vibration couplings under harmonic approximation, i.e., the Franck-Condon blockade effect, could be lifted in the case of symmetric double-well potentials. The removal of the Franck-Condon blockade effect is a result of the distribution of the ground vibrational wave function in the two wells. Such a feature also enables the Franck-Condon blockade effect to be restored by breaking the symmetry of the double-well potential. We further demonstrated that the special vibrational transition properties of asymmetric double-well potentials could enable the effective modulation of the charge transport properties of such molecular junctions in the Franck-Condon blockade region by inducing population in excited vibrational levels with external fields such as infrared excitation.