Super-poissonian noise, negative differential conductance, and relaxation effects in transport through molecules, quantum dots and nanotubes

TL;DR

This paper investigates charge transport in nanoscale systems like molecules and quantum dots, revealing how asymmetric coupling and relaxation influence conductance and noise, with implications for understanding electronic properties at the quantum level.

Contribution

It introduces a detailed model accounting for multiple energy levels, asymmetric coupling, and relaxation effects, predicting negative differential conductance and super-Poissonian noise in transport.

Findings

Negative differential conductance occurs with asymmetric lead coupling.

Super-Poissonian noise is observed under certain conditions.

Relaxation processes suppress these effects.

Abstract

We consider charge transport through a nanoscopic object, e.g. single molecules, short nanotubes, or quantum dots, that is weakly coupled to metallic electrodes. We account for several levels of the molecule/quantum dot with level-dependent coupling strengths, and allow for relaxation of the excited states. The current-voltage characteristics as well as the current noise are calculated within first-order perturbation expansion in the coupling strengths. For the case of asymmetric coupling to the leads we predict negative-differential-conductance accompanied with super-poissonian noise. Both effects are destroyed by fast relaxation processes. The non-monotonic behavior of the shot noise as a function of bias and relaxation rate reflects the details of the electronic structure and level-dependent coupling strengths.