Anomalous longitudinal magnetic field near the surface of copper conductors

Abstract
We have used ultracold atoms to characterize the magnetic field near the surface of copper conductors at room temperature carrying currents between 0.045 and 2 A. In addition to the usual circular field we find an additional, 1000–10 000 times smaller longitudinal field. The field changes its strength periodically with a period of 200–300 μ m.