Author Topic: The possibility of non-Maxwellian E field during superconducting transition  (Read 773 times)

Offline goran d

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If we switch a super-conductive disc between meissner and normal state by varying the strength of a magnetic field, something spins up the cooper pairs to produce the currents. We could assume that this is an E-field. This E-field is not according to Maxwell's Equations, since the charges are initially stationary and produce no field. This E-field moves in circles in the disc. So we could charge half the disc on one side positive, and the other half negative. And the extra-Maxwellian E-field produces force, not bound by Maxwell's Stress tensor. We can alter the charges on each side of the disc while switching the meissner effect on and off and produce a net force in one direction.

Online Phil Stooke

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Ok... let us know when you get it working.

Offline meberbs

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When running into something like this, your first reaction should be "maybe I don't understand this" not "I just overturned a field that has been studied in detail for over a century." https://xkcd.com/675/ (The mouseover text is especially relevant)

Conduction band electrons in a metal already are moving to begin with, so they don't need to be accelerated by an electric field, a magnetic field just bends their existing motion. (This starts at the superconducting transition in part because the lack of resistance means the electrons no longer are scattering off the nuclei and having their direction randomized.) Then a lot of complicated things happen as the patterns they move in cancel out the magnetic field inside the superconductor, and the changing magnetic field produces an electric field, plus forces between the electrons and the nuclei are relevant to some extent.

Offline Stormbringer

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Aren't there 2 dimensional topological superconductors now which would constrain at least some of the chaos? maybe have two such things stacked upon each other or held close but separated by some space that could have the sort of orientation the OP was speculating about?
When antigravity is outlawed only outlaws will have antigravity.

Offline meberbs

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The OP was talking about a violation of Maxwell's equations, and this isn't true. Without a violation of Maxwell's equations, the OP's idea won't go anywhere. (The main mistake was assuming conduction band electrons are stationary, I gave more detail than strictly necessary to point that out).

I haven't researched 2 dimensional superconductors (sounds interesting if I have time at some point) but if you are looking for a Maxwell's equations level derivation of how the currents initially form, it would still be difficult, because then you would need to account for the interactions with nuclei that generate the constraint, since Maxwell's equations don't reduce to 2D (cross products are inherently 3D).

Offline goran d

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I see more trouble for the idea that the magnetic field causes the charges to rotate. Since the force is the cross product of velocity and B field, the charges would have to shift outwards in order to be brought into rotation by the magnetic field. At first, this seems reasonable, as a gas with no resistance tends to expand, until it is stopped. (in our case by the electrostatic field). However, if we calculate the amount of distance that the charges would need to shift, and then find the static charge that would be accumulated due to the shift, it is enormous. The charges could not possibly shift by that much, it would create a breakdown in the surrounding air.

Offline meberbs

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I see more trouble for the idea that the magnetic field causes the charges to rotate. Since the force is the cross product of velocity and B field, the charges would have to shift outwards in order to be brought into rotation by the magnetic field. At first, this seems reasonable, as a gas with no resistance tends to expand, until it is stopped. (in our case by the electrostatic field). However, if we calculate the amount of distance that the charges would need to shift, and then find the static charge that would be accumulated due to the shift, it is enormous. The charges could not possibly shift by that much, it would create a breakdown in the surrounding air.
Try sharing these calculation details, maybe giving an order of magnitude for what you are talking about, and what specific starting assumptions you have so I can show you why you are wrong. (Because it is really, really unlikely that you are right.)

I don't even know what you mean by "charges would have to shift outward." Do you mean the electrons would have to have some velocity component perpendicular to the magnetic field? The electrons are constantly moving in all directions, so the magnetic field will naturally curve the paths of any electrons not moving exactly parallel to the magnetic field (basically all of them). This is happening even before the superconducting transition.

The effects are known, expected, and observed. If you want to challenge part of this, you need to show the detailed work on why they shouldn't be the case.

Offline goran d

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The attached file is how I work out the shift.

Offline goran d

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The attached file is how I work out the shift.

Uh-oh, seems i have made the erroneous assumption that B is constant.

Offline meberbs

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The attached file is how I work out the shift.

Uh-oh, seems i have made the erroneous assumption that B is constant.
Spatial and temporal variations in the B field are important in these calculations. (Especially temporal, as that generates E-fields).

Also, it slipped my mind entirely that the exclusion of an already present magnetic field is not expected of a perfect conductor. Superconductors have weird quantum effects that need to be accounted for that cause them to also act as a pefect diamegnet. In BCS theory, the electrons form Cooper pairs, allowing them to act as Bosons and form a Bose-Einstein condensate. I am not familiar enough with the details to explain why, but the quantum effects need to be accounted for on a macroscopic scale, which presumably means QED is required, not just pure Maxwell.

Also, for the high temperature superconductors, research is still ongoing to understand the mechanism, because quantum gets hard really quickly and the lattice structure of the ceramics in not trivial.

P.S. Looking at your original suggestion, it was to switch in an out of superconducting by varying the magnetic field, but this clearly generates an E-field by Maxwell's equations. I have been assuming that you are switching in and out by lowering the temperature which makes the question more interesting. Also worth looking up is Type II superconductors (which most high temperature ones are) since they have a range of magnetic field where they allow some penetration of magnetic fields that are strong enough but not too strong. This is not normal penetration as it is controlled by quantum mechanical vortices (again, I have not studied this thoroughly) and some interesting and useful effects result.