Tunneling broadening of vibrational sidebands in molecular transistors

TL;DR

This paper investigates how strong lead coupling affects vibrational sidebands in molecular transistors, revealing that tunneling broadening is suppressed, leading to sharper first Frank-Condon steps due to quantum effects.

Contribution

It introduces a novel expansion method showing the suppression of tunneling broadening by quantum effects and the Pauli principle in vibrationally coupled molecular transistors.

Findings

First Frank-Condon step is sharper than higher steps

Width of the first step is reduced by oscillator groundstate overlap

Tunneling broadening is strongly suppressed by quantum effects

Abstract

Transport through molecular quantum dots coupled to a single vibration mode is studied in the case with strong coupling to the leads. We use an expansion in the correlation between electrons on the molecule and electrons in the leads and show that the tunneling broadening is strongly suppressed by the combination of the Pauli principle and the quantization of the oscillator. As a consequence the first Frank-Condon step is sharper than the higher order ones, and its width, when compared to the bare tunneling strength, is reduced by the overlap between the groundstates of the displaced and the non-displaced oscillator.