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    Can someone explain to me why cooper pairs can travel through a conductor without losing any energy? And therefore why superconductors conduct electricity without any resistance?

    Thanks everyone!
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    (Original post by fatty_tbh)
    Because the resistivity drops to zero when the material is cooled below its critical tempreture
    Thanks, I get that bit, it's the part involving cooper pairs I'm struggling with.
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    to offer resistance then we'd need to change the momentum of one of the cooper pairs, say, but because of the cooperative nature of superconductivity - i.e. all the pairs are in the BCS wavefunction, which is like a coherent state, this is going to cost energy (roughly the SC gap delta) so scattering like this doesn't really take place

    if we could change ALL the pairs instantaneously into a new coherent state (with different total momentum) then this would be fine and could lead to resistance - however, we'd need some scattering mechanism which affects all of them at once, which doesn't really exist
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    (Original post by MC REN)
    to offer resistance then we'd need to change the momentum of one of the cooper pairs, say, but because of the cooperative nature of superconductivity - i.e. all the pairs are in the BCS wavefunction, which is like a coherent state, this is going to cost energy (roughly the SC gap delta) so scattering like this doesn't really take place

    if we could change ALL the pairs instantaneously into a new coherent state (with different total momentum) then this would be fine and could lead to resistance - however, we'd need some scattering mechanism which affects all of them at once, which doesn't really exist
    Sorry that's a little bit over my head! I'm only an A2 student, this is my own research project for A2 physics coursework, all I know so far is what a cooper pair is, in terms of electrons and phonons.
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    (Original post by Josh-H)
    Sorry that's a little bit over my head! I'm only an A2 student, this is my own research project for A2 physics coursework, all I know so far is what a cooper pair is, in terms of electrons and phonons.
    You won't be able to understand it. The proper treatment of it is grad level stuff. I thought MC REN did a pretty good job of explaining it, but it's a little complicated for an A2 project.

    Essentially, the cooper pairs act as bosons (even though the individual electrons are fermions). This allows them to form what is known as a coherent state. The below is from wiki, and is the best explanation I can find, I think you should be able to broadly understand that.

    An electron moving through a conductor will attract nearby positive charges in the lattice. This deformation of the lattice causes another electron, with opposite "spin", to move into the region of higher positive charge density. The two electrons then become correlated. There are a lot of such electron pairs in a superconductor, so that they overlap very strongly, forming a highly collective "condensate". Breaking of one pair results in changing of energies of remained macroscopic number of pairs. If the required energy is higher than the energy provided by kicks from oscillating atoms in the conductor (which is true at low temperatures), then the electrons will stay paired and resist all kicks, thus not experiencing resistance. Thus, the collective behaviour of "condensate" is a crucial ingredient of superconductivity.
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    (Original post by MC REN)
    to offer resistance then we'd need to change the momentum of one of the cooper pairs, say, but because of the cooperative nature of superconductivity - i.e. all the pairs are in the BCS wavefunction, which is like a coherent state, this is going to cost energy (roughly the SC gap delta) so scattering like this doesn't really take place

    if we could change ALL the pairs instantaneously into a new coherent state (with different total momentum) then this would be fine and could lead to resistance - however, we'd need some scattering mechanism which affects all of them at once, which doesn't really exist
    I've found a simpler explanation that makes more sense to me but I'm not sure it's quite correct?

    Physically, the Cooper pair is more resistant to vibrations within the lattice as the attraction to its partner will keep it 'on course' - therefore, Cooper pairs move through the lattice relatively unaffected by thermal vibrations (electron-phonon interactions) below the critical temperature.
    http://www.chm.bris.ac.uk/webproject...bcstheory.html

    The animations on there imply the cooper pair is still colliding with the atoms, doesn't that mean it would still be losing energy?
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    (Original post by Josh-H)
    I've found a simpler explanation that makes more sense to me but I'm not sure it's quite correct?



    http://www.chm.bris.ac.uk/webproject...bcstheory.html

    The animations on there imply the cooper pair is still colliding with the atoms, doesn't that mean it would still be losing energy?
    For your project it'd be fine to use similar wording to them, but you're right that the picture they've given isn't that good.

    The physical reason for no scattering is difficult to explain in terms of analogies and things, because fundamentally it is a quantum effect. But they shouldn't be colliding, no.

    There's a graphic on this site which is alright (under BCS) http://ffden-2.phys.uaf.edu/212_fall...rry/index.html
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    Apparently someone has discovered a state of matter called Superinsulator, which again is apparently explained in BCS.
    Its in Nature, but its publish date is some what dubious...

    It sounds like the Cooper Pairs form an incoherent state of sorts....
 
 
 
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