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Coherence caused by superconductivity

  1. Aug 14, 2007 #1
    why do different probability waves synchronize into one coherent wave at low temperatures? I'd like to research this but I don't know what this effect is called. Also, what is the quantum mechanical explanation for why the resistance in a super-conductive metal drops down to 0? Is it that the wavelength of the coherent wave after synchronization becomes long enough to allow individual electrons to quantum teleport through the positive nuclei in their paths? That doesn't sound right to me because "individual" electrons would no longer be distinguishable after they synchronized their quantum states. Would this newly formed coherent wave still diffract around the nuclei and interfere with itself or does it just travel through the nuclei in a ghostly fashion. I suspect the answer is closer to the latter since it seems to me that diffraction would decrease the current. Any help or reference is greatly appreciated. Thank you in advance
    Last edited: Aug 14, 2007
  2. jcsd
  3. Aug 16, 2007 #2
    As I understand it, electrons form pairs with collective integer spin. These therefore obey Bose-Einstein statistics rather than Fermi-Dirac statistics. The pairs thus are not scattered as they would be otherwise, and are free to flow without resistance.
  4. Aug 17, 2007 #3
    "electrons form pairs with collective integer spin"
    my question is why?

    "The pairs thus are not scattered as they would be otherwise"
    why do electrons with collective integer spin not get scattered by the nuclei? Is this tunneling or what?
  5. Aug 17, 2007 #4


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    To answer that, you need to understand the Cooper mechanism.

    Electrons can form bound pairs under a "many-body" effect using the material as the "glue". In conventional superconductors, the lattice phonons provide such a glue in the sense that the positive ions and other conduction electrons in the solid provide an "overscreening", so that any kind of net attractive force will result in a bound state. Refer to page 739 of Ashcroft and Mermin.

    No, no tunneling, at least not in this case. When the pairs form composite boson AND condenses into the BE state, than this becomes the general property of ANY BE condensate such as superfluidity, etc. You now have what is known as "long-range coherence", in which the "pairs" are now described by, naively, a series of plane waves that can propagate throughout the solid. Thus, it is this long-range coherence that provides the supercurrent.

  6. Sep 20, 2007 #5
    because by building the Cooper-pairs electrons can reduse their energy. look at "Fermy - see - instability". to see the calculation look in any theoretical book about superconductivity
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