Kondo effect in oscillating molecules

TL;DR

This paper investigates how molecular oscillations affect the Kondo effect in electronic transport through break-junctions, revealing that large tunneling modulation can lead to molecule displacement and reduced conductance.

Contribution

It introduces a two-channel Anderson model with position-dependent tunneling to analyze the impact of molecular oscillations on the Kondo regime.

Findings

Large tunneling modulation softens the confining potential.

Molecule tends to be attracted to one lead, decreasing conductance.

Numerical methods confirm the softening and displacement effects.

Abstract

We consider electronic transport through break-junctions bridged by a single molecule in the Kondo regime. We describe the system by a two-channel Anderson model. We take the tunneling matrix elements to depend on the position of the molecule. It is shown, that if the modulation of the tunneling by displacement is large, the potential confining the molecule to the central position between the leads is softened and the position of the molecule is increasingly susceptible to external perturbations that break the inversion symmetry. In this regime, the molecule is attracted to one of the leads and as a consequence the conductance is small. We argue on semi-classical grounds why the softening occurs and corroborate our findings by numerical examples obtained by Wilson's numerical renormalization group and Schoenhammer-Gunnarsson's variational method.