Vibration-mediated resonant tunneling and shot noise through a molecular quantum dot

TL;DR

This paper models vibration-mediated electron tunneling and shot noise in a molecular quantum dot, revealing how electron-phonon interactions cause negative differential conductance and super-Poissonian noise.

Contribution

It introduces a rate equation approach to analyze nonequilibrium vibrational effects on tunneling and noise in a molecular quantum dot with asymmetric coupling.

Findings

Negative differential conductance can be delayed or advanced due to vibrational effects.

Super-Poissonian shot noise arises from electron-phonon-induced cascades.

Vibrational interactions significantly influence current-voltage characteristics.

Abstract

Motivated by a recent experiment on nonlinear tunneling in a suspended Carbon nanotube connected to two normal electrodes [S. Sapmaz, {\it et al}., Phys. Rev. Lett. {\bf 96}, 26801 (2006)], we investigate nonequilibrium vibration-mediated sequential tunneling through a molecular quantum dot with two electronic orbitals asymmetrically coupled to two electrodes and strongly interacting with an internal vibrational mode, which is itself weakly coupled to a dissipative phonon bath. For this purpose, we establish rate equations using a generic quantum Langevin equation approach. Based on these equations, we study in detail the current-voltage characteristics and zero-frequency shot noise, paying special attention to the advanced or postponed of the appearance of negative differential conductance and super-Poissonian current noise resulting from electron-phonon-coupling induced {\em selective unidirectional cascades of single-electron transitions}.