Spin versus charge noise from Kondo traps

Abstract

Magnetic and charge noise have common microscopic origin in solid state devices, as described by a universal electron trap model. In spite of this common origin, magnetic (spin) and charge noise spectral densities display remarkably different behaviours when many-particle correlations are taken into account, leading to the emergence of the Kondo effect. Our numerical renormalization group results indicate that while spin noise is a universal function of the Kondo temperature, charge noise remains well described by single-particle theory even when the trap is deep in the Kondo regime. This difference survives even in the presence of disorder, showing that noise can be more manageable in devices that are sensitive to magnetic (rather than charge) fluctuations and that the signature of the Kondo effect can be observed in spin noise spectroscopy experiments.

9 pages, 6 figures; To appear in PRB. Revised version: includes derivation of exact sum rules, analytical approximation for the spin noise, and additional details of the NRG calculation