Phonon-assisted tunneling and two-channel Kondo physics in molecular junctions

TL;DR

This paper investigates how vibrational modes influence Kondo physics in molecular junctions, revealing a phonon-assisted two-channel Kondo effect with non-Fermi-liquid behavior at critical coupling strengths.

Contribution

It introduces a theoretical model showing phonon-assisted tunneling induces a two-channel Kondo effect with non-Fermi-liquid fixed points in molecular conductors.

Findings

Non-Fermi-liquid behavior observed at low temperatures.

Critical points depend on phonon-mediated coupling strength.

Distinct thermodynamic and conductance signatures of the two-channel Kondo state.

Abstract

The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. We present theoretical results for a single molecule in the Kondo regime connected to left and right metallic leads, creating the usual coupling to a conduction channel with left-right parity ("even"). A center-of-mass vibrational mode introduces an additional, phonon-assisted, tunneling through the antisymmetric ("odd") channel. A non-Fermi liquid fixed point, reminiscent of the two-channel Kondo effect, appears at a critical value of the phonon-mediated coupling strength. Our numerical renormalization-group calculations for this system reveal non-Fermi-liquid behavior at low temperatures over lines of critical points. Signatures of this strongly correlated state are prominent in the thermodynamic properties and in the linear conductance.