Excess noise in Al x Ga 1 − xAs/GaAs based quantum rings

Cross-correlated noise measurements are performed in etched Al x Ga 1 − xAs/GaAs based quantum rings in equilibrium at a bath temperature of T bath = 4.2 K. The measured white noise exceeds the thermal (Johnson–Nyquist) noise expected from the measured electron temperature T e and the electrical resistance R. This excess part of the white noise decreases as T bath increases and vanishes for T bath ≥ 12 K. Excess noise is neither observed if one arm of a quantum ring is depleted of electrons nor in one-dimensional-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.