IS THE STATIC MAGNETIC VECTOR POTENTIAL SCREENED BY A THICK SUPERCONDUCTING SHIELD

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Abstract

In 1986 Tonomura and his co-workers reported the results of a test for the existence of the magnetic Aharonov-Bohm (AB) effect using permalloy toroids with a superconducting niobium coating. Classical Maxwell theory suggests that the group may have been able to observe the AB effect only because their superconducting shield was quite thin (2.5 penetration depths), and that, had a very thick shield been used, no AB effect would have been observable. However, orthodox quantum mechanics predicts that a static vector potential penetrates a superconducting shield of any thickness in cases where the magnetic flux inside the sample is an odd integer times h/2 e. Regardless of which view is correct, it is argued in this paper that a superconductor only screens leakage or fringing field to the extent that it screens vector potential, so that there are doubts that the experiment answered the critics of earlier experiments, as was claimed.

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