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

TL;DR

This paper theoretically examines how capacitance and tunneling asymmetries influence Coulomb blockade edges and Kondo peaks in non-equilibrium transport through molecular quantum dots, revealing significant renormalization effects.

Contribution

It introduces a detailed analysis of asymmetry effects on quantum dot transport using the Non-Crossing-Approximation and proposes a phenomenological model for experimental comparison.

Findings

Coulomb blockade edges and Kondo peaks are strongly renormalized by asymmetries.

Basic Coulomb blockade theory requires careful application when Kondo physics is involved.

A simple phenomenological model can semi-quantitatively reproduce numerical results.

Abstract

We investigate theorerically the non-equilibrium 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 Non-Crossing-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, expecially when Kondo physics is at play. In order to help comparison of theory to experiments, we also propose a simple phenomenological model which reproduces semi-quantitatively the Coulomb blockade edges that were numerically computed from the NCA in all regimes of parameters.