Blocking-state influence on shot noise and conductance in quantum dots

TL;DR

This paper studies how blocking states in carbon nanotube quantum dots affect shot noise and conductance, revealing electron bunching and negative differential conductance through combined measurements and simulations.

Contribution

It demonstrates the role of blocking states in quantum dots and provides a combined experimental and theoretical analysis of their impact on transport properties.

Findings

Observation of negative differential conductance.

Detection of super-Poissonian noise indicating electron bunching.

Numerical simulations matching experimental data.

Abstract

Quantum dots (QDs) investigated through electron transport measurements often exhibit varying, state-dependent tunnel couplings to the leads. Under specific conditions, weakly coupled states can result in a strong suppression of the electrical current and they are correspondingly called blocking states. Using the combination of conductance and shot noise measurements, we investigate blocking states in carbon nanotube (CNT) QDs. We report negative differential conductance and super-Poissonian noise. The enhanced noise is the signature of electron bunching, which originates from random switches between the strongly and weakly conducting states of the QD. Negative differential conductance appears here when the blocking state is an excited state. In this case, at the threshold voltage where the blocking state becomes populated, the current is reduced. Using a master equation approach, we provide numerical simulations reproducing both the conductance and the shot noise pattern observed in our measurements.