Re: flux +- quantization

[John Denker <jsd@MONMOUTH.COM>]

At 01:07 PM 10/4/99 -0400, Chuck Britton wrote:
> But isn't it true that magnetic fields are quantized and that
> superconductors are 'sensitive' to single quantum changes???

1a) The *flux* within a superconducting is quantized.

1b) The *flux* penetrating a type-II superconductor does so in the form of
quantized vortices of current.

1c) If you look closely at the passage of a flux-line from inside the ring
to outside, there will be a time when flux line is within the substance of
the ring, neither fully inside nor fully outside, so the notion of flux
quantization partially breaks down at this point.

1d) In a non-superconducting ring, you can have any amount of flux you want
-- no quantization.



2) The magnetic field _per se_ is never quantized.



Bottom line: the quantization is not a property of the flux.  You can think
of it as a property of the superconductor.

______________________________________________________________
copyright (C) 1999 John S. Denker             jsd@monmouth.com