Impact of capacitance and tunneling asymmetries on Coulomb blockade edges and Kondo peaks in nonequilibrium transport through molecular quantum dots

Abstract

We investigate theoretically the nonequilibrium transport through a molecular quantum dot as a function of gate and bias voltage, taking into account the typical situation in molecular electronics. In this respect, our study includes asymmetries both in the capacitances and tunneling rates to the source and drain electrodes, as well as an infinitely large charging energy on the molecule. Our calculations are based on the out-of-equilibrium noncrossing approximation (NCA), which is a reliable technique in the regime under consideration. We find that Coulomb blockade edges and Kondo peaks display strong renormalization in their width and intensity as a function of these asymmetries, and that basic expectations from Coulomb blockade theory must be taken with care in general, especially when Kondo physics is at play. In order to help comparison of theory to experiments, we also propose a simple phenomenological model which reproduces semiquantitatively the Coulomb blockade edges that were numerically computed from the NCA in all regimes of parameters.