Excess noise in Al${}_\text{x}$Ga${}_\text{1-x}$As/GaAs based quantum rings

TL;DR

This study investigates excess white noise in AlGaAs/GaAs quantum rings at low temperatures, revealing it originates from phase-coherent electron correlations and diminishes with increasing temperature.

Contribution

It provides the first measurement of excess noise in quantum rings and proposes a model linking it to phase-coherent electron correlations.

Findings

Excess noise decreases with increasing bath temperature and vanishes above 12 K.

No excess noise observed when one arm of the quantum ring is depleted or in similar 1D constrictions.

A model suggests excess noise arises from correlated noise sources mediated by phase coherence.

Abstract

Cross-correlated noise measurements are performed in etched Al${}_\text{x}$Ga${}_\text{1-x}$As/GaAs based quantum rings in equilibrium at bath temperature of $T_\text{bath}=4.2\text{ K}$. The measured white noise exceeds the thermal (Johnson-Nyquist) noise expected from the measured electron temperature $T_\text{e}$ and the electrical resistance $R$. This excess part of the white noise decreases as $T_\text{bath}$ increases and vanishes for $T_\text{bath}\geq 12\text{ K}$. Excess noise is neither observed if one arm of a quantum ring is depleted of electrons nor in 1D-constrictions that have a length and width comparable to the quantum rings. A model is presented that suggests that the excess noise originates from the correlation of noise sources, mediated by phase-coherent propagation of electrons.