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Superconductor curiousities

  1. Mar 3, 2004 #1

    Cliff_J

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    Ok, I can't exactly run out to the store and put some of these in my freezer to experiment with (hurry up guys :smile:), so here's just some questions I was thinking about.

    - Superconductors would have very near zero resistance (part of their definition) so would that mean that the current carrying capabilities would be incredibly large as well? Assuming we don't heat them past their range of superconductivity of course. But we would eventually still reach some level of saturation because we wouldn't have enough free electrons to participate in our signal flow, even if this was like an absurd amount like 500A on a 24ga wire or something.

    - What impedance characteritics are to be expected from superconductors? I would guess they would drop as well.

    - Are these materials suitable for replacements for semiconductors where they can be doped to have N and P junctions or similar functioning equivalents?

    - Any information on the exact reason why we need to approach 0K for super-conductors to work?

    Thanks in advance.

    Cliff
     
  2. jcsd
  3. Mar 3, 2004 #2
    SC does have critical current density, ~10^4 amps, above which SC disappears. There are hole and electron doped superconductors, but most High Tc material is hole doped. A group in Japan tried to make a pn junction out of SC material, but it did not rectify. Although you can make some neat devices based on the josephson effect. Thermal Flucations kill electron pairing at high temperatures.

    JMD
     
  4. Mar 3, 2004 #3

    Cliff_J

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    I found more info, must've typo'd in my first searches.
    http://www.ornl.gov/info/reports/m/ornlm3063r1/pt3.html

    Hmmm, those predictions a few years ago of room-temperature super-conductors seem a little further off in the future than they were made out to be in the magazines....
     
  5. Mar 3, 2004 #4

    turin

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    Yes.




    Resistance is impedence, so, I'll assume that you meant reactance. I would not expect this to drop. I would expect the impedance to become purely reactive in superconduction (so that the impedance vector would collapse onto its projection on the imaginary axis).




    Speculation on my part:
    Random thermal excitations de-pair electrons.
     
  6. Mar 3, 2004 #5

    chroot

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    The free electron gas must undergo Bose-Einstein condensation, a delicate phase transition that is destroyed by thermal vibrations.

    - Warren
     
  7. Mar 3, 2004 #6
    Yeah, I just don’t know why they’re calling it BEC (can’t deny that there’s no similarity but....), when they can’t really be all in same state place time, like bosons, after all they’re fermions, and I think that “fermionic condensate” is OK.

    p.s. I think that all experiments they conduced, involved nuclei, not whole atoms, they done it without electrons (they haven’t mentioned it). Correct me if I’m wrong.


    Edit: sorry it’s little bit off course/topic – In lines up I was referring to experiment with potassium atoms chilled to fermionc condensate – and I overlooked that they paired up atoms into molecules with net integer spin – in that way obtaining bosons and packing them into BEC
     
    Last edited: Mar 3, 2004
  8. Mar 3, 2004 #7

    chroot

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    Yep, the electrons in a superconductor form Cooper pairs, each of which acts like an "unlocalized" boson.

    - Warren
     
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