Vibrationally-mediated molecular transistors

TL;DR

This paper explores how vibrational modes influence electronic transport in molecular transistors, revealing resonance effects, current suppression, and potential for highly sensitive molecular sensors.

Contribution

It introduces a combined analytical and numerical study of vibrationally-mediated transport, demonstrating the potential for novel molecular transistor functionalities.

Findings

Resonant enhancement of current at phonon frequencies

Observation of phonon absorption and emission peaks

Identification of a Frank-Condon blockade effect

Abstract

We investigate the steady-state electronic transport through a suspended dimer molecule coupled to leads. When strongly coupled to a vibrational mode, the electron transport is enhanced at the phonon resonant frequency and higher-order resonances. The temperature and bias determines the nature of the phonon-assisted resonances, with clear absorption and emission peaks. The strong coupling also induces a Frank-Condon-like blockade, suppressing the current between the resonances. We compare an analytical polaron transformation method to two exact numerical methods: the Hierarchy equations of motion and an exact diagonalization in the Fock basis. In the steady--state, our two numerical results are an exact match and qualitatively reflect the main features of the polaron treatment. Our results indicate the possibility of a new type of molecular transistor or sensor where the current can be extremely sensitive to small changes in the energies of the electronic states in the dimer.