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

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 $T_{\text{bath}}\ge 12\text{ K}$. 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.

4 pages, 4 figures