Magnetic near fields as a probe of charge transport in spatially dispersive conductors

TL;DR

This paper investigates how magnetic field fluctuations above conductors with spatial dispersion reveal charge transport properties, showing that the mean free path influences near-field coherence and noise, with implications for atom chip experiments.

Contribution

It provides a detailed calculation of magnetic near fields considering nonlocal responses, highlighting the impact of charge transport regimes on near-field fluctuations and coherence.

Findings

Reduced noise spectrum below the mean free path in nonlocal conductors

Mean free path sets a lower limit to near-field coherence length

Short-distance behavior applies across various materials including semiconductors and superconductors

Abstract

We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behavior is common to a wide range of materials, covering also semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturized atom traps and matter wave interferometers.