Transport properties of a molecule embedded in an Aharonov-Bohm interferometer

TL;DR

This paper explores how phonons influence electron transport in a molecular Aharonov-Bohm interferometer, revealing Fano resonances, charge Kondo effects, and the impact of electron-phonon interactions on conductance.

Contribution

It provides a theoretical analysis of phonon effects on molecular transport, including the emergence of Fano resonances and charge Kondo phenomena, using Numerical Renormalization Group methods.

Findings

Fano resonances arise from interference between Kondo state and direct path.

Strong electron-phonon interaction can induce an effective attractive interaction, promoting charge Kondo effect.

Gate voltage tuning can restore the Kondo resonance suppressed by electron-hole symmetry breaking.

Abstract

We theoretically investigate the transport properties of a molecule embedded in one arm of a mesoscopic Aharonov-Bohm interferometer. Due to the presence of phonons the molecule level position ($\epsilon_d$) and the electron-electron interaction ($U$) undergo a \emph{polaronic shift} which affects dramatically the electronic transport through the molecular junction. When the electron-phonon interaction is weak the linear conductance presents Fano-line shapes as long as the direct channel between the electrodes is opened. The observed Fano resonances in the linear conductance are originated from the interference between the spin Kondo state and the direct path. For strong enough electron-phonon interaction, the electron-electron interaction is renormalized towards negative values, {\it i.e.} becomes effectively attractive. This scenario favors fluctuations between the empty and doubly occupied charge states and therefore promotes a charge Kondo effect. However, the direct path between the contacts breaks the electron-hole symmetry which can efficiently suppress this charge Kondo effect. Nevertheless, we show that a proper tuning of the gate voltage is able to revive the Kondo resonance. Our results are obtained by using the Numerical Renormalization approximation to compute the electronic spectral function and the linear conductance.