Theory of high bias Coulomb Blockade in ultrashort molecules

TL;DR

This paper develops a many-electron master-equation approach to explain Coulomb Blockade effects in ultrashort molecules, revealing phenomena that traditional methods cannot capture, especially in weak coupling regimes.

Contribution

It introduces a comprehensive many-electron framework using exact diagonalization to accurately model Coulomb Blockade in ultrashort molecules, surpassing traditional SCF approaches.

Findings

Explains vanishing zero bias conductance and sharp current onsets.

Shows importance of strong electron correlations in transport.

Demonstrates limitations of traditional SCF methods.

Abstract

We point out that single electron charging effects such as Coulomb Blockade (CB) and high-bias staircases play a crucial role in transport through single ultrashort molecules. A treatment of Coulomb Blockade through a prototypical molecule, benzene, is developed using a master-equation in its complete many-electron Fock space, evaluated through exact diagonalization or full Configuration Interaction (CI). This approach can explain a whole class of non-trivial experimental features including vanishing zero bias conductances, sharp current onsets followed by ohmic current rises, and gateable current levels and conductance structures, most of which cannot be captured even qualitatively within the traditional Self Consistent Field (SCF) approach coupled with perturbative transport theories. By comparing the two approaches, namely SCF and CB, in the limit of weak coupling to the electrode, we establish that the inclusion of strong-correlations within the molecule becomes critical in addressing the above experiments. Our approach includes on-bridge-correlations fully, and is therefore well-suited for describing transport through short molecules in the limit of weak coupling to electrodes.