Why do superconductors superconduct current?

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  • #26
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Of course they dont, not the classical way. You dont need to correct me on this point, i know these things very very well and I have never stated that they orbit like planets round the sun. The diamagnetism are due to the QM 'ortibs 'electrons have in atoms.
that doest explain why you think that superconductivity causes diamagnetism. how does superconductivity effect electron spin?
 
  • #27
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Because the paring state has a lower energy than the single-particle state. This is what Leon Cooper showed for 2 electrons just above the Fermi energy, and what was extended in the BCS theory for the Fermi gas itself.

Zz.
i know that. the question becomes why do they not form these cooper pairs in non-superconductors?
 
  • #28
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Er.. did I have a weird deja vu, or didn't you just repeated yourself here?

Zz.
 
  • #29
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diamagnetism is the tendency of the electrons to orient their spin opposite that of the magnetic field and thereby cancel it out. that is exactly what electrons in cooper pairs are doing therefore i believe that diamagnetism (or whatever causes diamagnetism) is what causes electrons to form pairs.
If this is true, then the paring strength of ALL superconductors would be the same, because it only depends on the spin-spin coupling strength. We know that this isn't true, and that there is a wide range of coupling strength simply based on the size of the energy gap in tunneling spectroscopy. Furthermore, you would have an interesting time reconciling that scenario with the isotope effect.

Zz.
 
  • #30
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Er... they don't? I'm not sure where this requirement for diamagnetism as the precursor to superconductivity comes from. I never made such statement.

Zz.
you say that cooper pairs explain superconductivity. are you now saying that they form in non-superconductors?

dont think that i dont know that i am being trolled.
 
  • #31
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The usual treatment of the diamagnetism of atoms and ions employs the Larmor theorem: In a magnetic field the motion of the electrons around a central nucleus is, to the first order in B, the same as a possible motion in the absence of B except for the superposition of a precession of the electrons with angular frequency:

[tex] \omega = eB/2mc [/tex]

This was from Kitell, diamagnetism is due to atomic electrons tending to loop around the applied B-field, i.e it is related to their orbital angular momenta. And they are orbiting so that the applied B field is cancelled (not completley).

Paramagnetism is the tital Atomic spin J that wants to be allinged with the B-field.

Pauli paramagnetism is due to the conduction electrons intrinsic spin wanting to be allinged with the applied B-field.

Iam not gonna write in this thread more, you are just annoying me grandpa. Cite scienfic litterature instead of coming with your non-sence speculations here. Superconductivity and diamagnetism are very well understood. You just seem to lack the basics.

Just read this:
"i know that. the question becomes why do they not form these cooper pairs in non-superconductors?"

Maybe becase cooper pairs gives you SC ?
 
  • #32
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you say that cooper pairs explain superconductivity. are you now saying that they form in non-superconductors?

dont think that i dont know that i am being trolled.
No, if anyone is trolling, it appears to be you.

Where did I say that cooper pairs form in non-superconductors {even if there ARE recent results that show paring in insulators}? Are all materials that eventually become superconducting HAVE to be a diamagnet? High Tc cuprates are antiferromagnetic, save for the dopants.

The diamagnetism (or perfect diamagnetism) in superconductors occurs AFTER it has undergone such transition. Even then, this is not due to individual spins, but rather due to the whole superfluid responding to the external magnetic field. So I have no clue where this requirement for diamagnetism to be present FIRST before superconductivity can set in. Can you specifically point out in the BCS theory where this is required?

Zz.
 
  • #33
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If this is true, then the paring strength of ALL superconductors would be the same, because it only depends on the spin-spin coupling strength. We know that this isn't true, and that there is a wide range of coupling strength simply based on the size of the energy gap in tunneling spectroscopy. Furthermore, you would have an interesting time reconciling that scenario with the isotope effect.

Zz.
i am not suggesting that electrons simply form pairs and that causes diamagnetism and superconductivity.

if we think of each electron as a small magnet and if we could somehow cancel out the charge then the two electrons would indeed be attracted to one another and would couple with a certain amount of strength but the resulting pair would still have a magnetic field because the spins would be parallel. in cooper pairs the spins are opposite therefore the magnetic fields cancel out entirely. i assume therefore that the bonding is due to the same mysterious force that causes diamagnetic materials to generate magnetic fields that oppose and cancel out any externally applied magnetic fields. i dont see why the coupling strength would be the same for all superconductors.
 
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  • #34
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No, if anyone is trolling, it appears to be you.

Where did I say that cooper pairs form in non-superconductors {even if there ARE recent results that show paring in insulators}? Are all materials that eventually become superconducting HAVE to be a diamagnet? High Tc cuprates are antiferromagnetic, save for the dopants.

The diamagnetism (or perfect diamagnetism) in superconductors occurs AFTER it has undergone such transition. Even then, this is not due to individual spins, but rather due to the whole superfluid responding to the external magnetic field. So I have no clue where this requirement for diamagnetism to be present FIRST before superconductivity can set in. Can you specifically point out in the BCS theory where this is required?

Zz.

i asked you why electrons form cooper pairs in superconductors and not in non-conductors. you never answered my question except to give a flippant response about it being a lower energy state (which is self-evident).

i am the one saying that diamagnetism comes first. that it causes the electrons to form cooper pairs.
 
  • #35
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i asked you why electrons form cooper pairs in superconductors and not in non-conductors. you never answered my question except to give a flippant response about it being a lower energy state (which is self-evident).
I'm not being flippant. I thought by mentioning the Fermi energy, it is obvious that it requires charge charriers!

i am the one saying that diamagnetism comes first. that it causes the electrons to form cooper pairs.
Then you shouldn't be asking me about the diamagnetism requirment since this is your "model".

granpa said:
i am not suggesting that electrons simply form pairs and that causes diamagnetism and superconductivity.

if we think of each electron as a small magnet and if we could somehow cancel out the charge then the two electrons would indeed be attracted to one another and would couple with a certain amount of strength but the resulting pair would still have a magnetic field because the spins would be parallel. in cooper pairs the spins are opposite therefore the magnetic fields cancel out entirely. i assume therefore that the bonding is due to the same mysterious force that causes diamagnetic materials to generate magnetic fields that oppose and cancel out any externally applied magnetic fields. i dont see why the coupling strength would be the same for all superconductors.
Then you are formulating your own personal theory. You should also not ignore TRIPLET superconductors such as the ruthenates which completely destroys your scenrios of cooper pairs made up only of electrons with "opposite spins".

The "bonding" in conventional superconductors is due to phonons. You see the phonon coupling clearly in McMillen-Rowell reconstruction of in the tunneling density of states, in the electron-phonon coupling strength, and in the isotope effect (which you have not addressed).

Zz.
 
  • #36
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I'm not being flippant. I thought by mentioning the Fermi energy, it is obvious that it requires charge charriers!
.
i can see how fermi energy could play a role. whats interesting to me is where the energy comes from for a diamagnetic material to exclude an externally applied magnetic field.
not sure what 'it' is that requires charge carriers.

my mistake if you werent being flippant. the 'Zz' at the bottom of your posts doesnt help much. its used by a well know troll on craigslist.

Then you shouldn't be asking me about the diamagnetism requirment since this is your "model".
.
you must be one of those people that takes every word people say literally. i was simply asking about superconductors. i used the word diamagnetic as a hint. it was supposed to stimulate discussion.

Then you are formulating your own personal theory. You should also not ignore TRIPLET superconductors such as the ruthenates which completely destroys your scenrios of cooper pairs made up only of electrons with "opposite spins".

The "bonding" in conventional superconductors is due to phonons. You see the phonon coupling clearly in McMillen-Rowell reconstruction of in the tunneling density of states, in the electron-phonon coupling strength, and in the isotope effect (which you have not addressed).

Zz.
triplets? not sure i buy that. i think it is the complete absence of the magnetic field that allows the electrons to move without resistance. except of course for things like molecule size wires which i heard can sometimes exhibit superconductor-like properties.

phonons. thats interesting. but i figured it had to be something. like i said i dont think its a simple matter of the electrons bonding magnetically.
 
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  • #37
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i can see how fermi energy could play a role. whats interesting to me is where the energy comes from for a diamagnetic material to exclude an externally applied magnetic field.
not sure what 'it' is that requires charge carriers.

my mistake if you werent being flippant. the 'Zz' at the bottom of your posts doesnt help much. its used by a well know troll on craigslist.



you must be one of those people that takes every word people say literally. i was simply asking about superconductors. i used the word diamagnetic as a hint. it was supposed to stimulate discussion.



triplets? not sure i buy that. i think it is the complete absence of the magnetic field that allows the electrons to move without resistance. except of course for things like molecule size wires which i heard can sometimes exhibit superconductor-like properties.

phonons. thats interesting. but i figured it had to be something. like i said i dont think its a simple matter of the electrons bonding magnetically.
There's so many things wrong in here, I don't know where to start.

1. Please familiarize yourself with the ruthenates superconductor.

2. Please familiarize yourself with BCS superconductivity AND the phonon mechanism. This should NOT be a "surprise" to you when your intention is to come up with your own personal theory.

3. No one is claiming any "electrons bonding magnetically" except you.

4. This thread has deteriorated in unverified personal speculation that is in violation of the PF Guidelines. Therefore, it is done. If the OP has any follow-up question, he/she is welcome to PM me and I will reopen the thread.

Zz.
 

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