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What is superfluidity/superconductivity?

  1. Aug 3, 2004 #1
    could somebody give me insight on the subject please. :approve:
     
  2. jcsd
  3. Aug 4, 2004 #2

    ZapperZ

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    Superconductivity is the flow of electrical current without any resistance (zero resistivity).

    Superfludity is the flow of the fluid itself without any resistance (zero viscosicity).

    Other than that, I'm not sure what level of "insight" you were asking for...

    Zz.
     
  4. Aug 4, 2004 #3
    The interesting thing is that when we mean zero, we mean zero.
     
  5. Aug 4, 2004 #4

    ZapperZ

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    Exactly! These phenomena aren't achieved in a gradual fashion as one varies various relevant parameters like temperature, and the quantities such as electrical resistance just doesn't become smaller and smaller until they are too small to measure (but still non-zero in principle). They are an abrupt phase transition in which the material has undergone a definite change in state. So quantities such as electrical resistance, viscosity, and bulk magnetization would drop abruptly as one crosses over the critical parameter.

    Zz.
     
  6. Aug 4, 2004 #5
    so can this be acheved over a long period of time. I heard that you attain supeconductivity when you cool certain materials at super low temperatures. How would superfluidity work, and how is it tested?
     
  7. Aug 4, 2004 #6
    Superfluidity comes about when all the atoms of helium in a bucket of liquid helium
    become one big atom! This happens because the Helium atoms change from being
    spin 1/2 particles to spin 1 and obey bose-einstein statistics instead of fermi -dirac statistics.The helium climbs out of the bucket without any help.
     
  8. Aug 4, 2004 #7
    It can last for as long as you care to keep the stuff cold enough. A few degrees Kelvin or less for superfluid helium. For superconductivity, it depends on the material. A few Kelvins to about 120 K I think. At least one experiment has maintained superconductivity for more than a year.
     
  9. Aug 5, 2004 #8

    Galileo

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    I quote from Kittel's "Intro. to Solid State Physics":

     
  10. Aug 5, 2004 #9
    that explains a lot, but could you explain the last sentince. Im not sure what you mean.
     
  11. Aug 5, 2004 #10

    ZapperZ

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    This is just purely a friendly advice, so you can take it for whatever it is worth. Since I participated in this string, I don't want my "silence" in commenting on certain things to imply my implicit approval to what was said.

    You should be more discriminating in the sources to pay attention to on here. Let's just say that in this string, both Gonzolo and Galileo have given excellent responses, not simply because they agreed with me or I agreed with them, but because they have given you basically "textbook" and accepted physics answers, which I think is what you were looking for. [I will refrain from evaluating my own responses].

    I'm sure you're smart enough to draw your own conclusion from that. I hate to think you get strung along on some wild goose chase on something and end up with what you believe is an accepted physics, when in fact it might not.

    Zz.
     
  12. Aug 5, 2004 #11
  13. Aug 6, 2004 #12

    ZapperZ

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    Funny you should mention that, because I know Chris Homes very well (we used to be in the same division at BNL while I was there), and I e-mailed him last week when the Nature paper came out that now he and Newton have something in common! :)

    [The paper got wide publicity at the BNL homepage. See
    http://www.bnl.gov/bnlweb/pubaf/pr/2004/bnlpr073004.htm ]

    Frankly, it can't. However, it provides a huge piece of the puzzle in the sense that 3 different parameters are somehow tied to each other across (and this is a MAJOR point) different types of materials and across different doping levels.

    The problem with high Tc superconductors is that there are simply too many things going on that we sometime don't know which parameters are important and which ones are the red herrings. Is the pseudogap a signature of an important precursor to superconductivity, or is it merely competing with superconductivity and thus, not a part of it? This paper clearly points out that these three parameters ARE important, they are not red herrings, and not only that, it also describes how they relate to each other independent of what high-Tc compound you look at! This is important because we can also extrapolate the relationship to predict the parameter of subsequent material i.e. what does something with Tc of room temperature should have.

    It is times like these that I often miss not still working in condensed matter.... <sigh>

    Zz.

    Addendum: I forgot to mention that the technique used in this analysis is part of optical conductivity measurement, i.e. shining light onto a material and see what part gets transmitted and what gets reflected. This is one way of determining the superfluid density in the superconductor. This technique would be useless and meaningless if light has no E and B field as described within classical E&M and QM, and the results and conclusion we obtain about the material would be a total garbage <an obvious reference to a number of other strings on PF>.
     
    Last edited: Aug 6, 2004
  14. Aug 6, 2004 #13
    thanx for the insightfull answers.
     
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