Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

High-temperature superconductors

  1. May 31, 2005 #1
    Okay - I understand the idea of why superconductors work (i hope i do - it was a while ago I learned it) - namely by two electrons of 1/2 integer spin obeying Fermi-Dirac statistics, forming a pair of electrons than can behave in some circumstances like a single particle with integer spin. This 'new' particle is not constrained by the exclusion principle and also it obeys the Bose-Einstein statistics that describe the behaviour of photons (in the quantum mechanical terms).

    However - I was always under the impression that above a temperature (dependant on the material) typically around 0-10K, the electron pairing is split up. So, I was wondering how one explains the idea of the results of Bednorz and Mueller when they found superconductive properties at around 30k? I hadn't heard about this result until recently and it confused me! Any ideas any one?!

    -ben
     
    Last edited by a moderator: May 31, 2005
  2. jcsd
  3. Jun 1, 2005 #2
    They (copper pairs) don't behave as photons, but they do obey boson commutation relations. Low Tc materials that are conventional BCS superconductors do have a upper Tc, of around 17K. The HTSC are still a mystery.
     
  4. Jun 1, 2005 #3

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    What you neglected to include in your description above is the "glue" that causes the electron to pair up.

    In conventional superconductors, the "glue" here are phonons, i.e. the quantized lattice vibrations. What we know of these phonons caused us to predict back then that the coupling strength that they can provide will not allow us to get superconductivity much beyond 30 K.

    High Tc superconductors (achieving Tc up to 135K under atm. pr) means that either our understanding of phonons are incomplete, or there is a new glue that binds the electrons together (such as spinons). Spin fluctuations have had many supporting evidence, but there are still no consensus on the exactly mechanism.

    In any case, this question belongs more in the condensed matter part of PF, so that is where it will be moved to.

    Zz.
     
  5. Jun 1, 2005 #4
    Yes I didn't mention phonons because I'm stupid and didn't consider them, bit daft of me really.

    Has there been any work done on the reason for high-temp superconductors?

    And equally interestingly, has any more work been done on their applications - especially as 135K is a much more economical temperature than 30K to keep the material cool at for I understood that the work on superconductors was not considered feesable due to temperature. However, if that temperature is raised then the use of the superconductor and its properties (virtually no resistance + a blocking out of magnetic fields) would definitely become more important wouldn't they - especially to the military etc?

    - Ben
     
  6. Jun 1, 2005 #5

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    During its heydays, roughly 2000 papers PER WEEK were published on HTS. So yes, I would day that a lot of work has been done (and continues to be done) on the physics and origin of its high Tc.

    While YBCO has been used in various applications, the use of HTS is being hindered technologically primarily because of its low current density. I will flat out say that these family of materials are more fascinating in the physics sense. It has ramifications throughout condensed matter physics because at the very fundamental level, it tests how strongly-correleted electron systems behave and how well we can describe them. Such knowledge is the essence of condensed matter physics. Thus, this system has such rich physics, I don't think we'll ever be done with it, even after we discover the 'glue'.

    Zz.

    P.S. You should not do multiple post of identical question.
     
    Last edited: Jun 1, 2005
  7. Jun 2, 2005 #6
    Thre is some commercial activity with HTS. For example, American Superconductors is making HTS cables. There are some another, non-wire application as well:
    http://superconductors.org/Links.htm
     
  8. Jun 18, 2005 #7
    protonic high-T superconductors

    Re really :surprised high-T superconductivity, you may be interested in a recent report in New Scientist (May 7th) on saturated transition metal hydrides that contain Cooper pairs made of protons rather than electrons. If large chunks of these substances can really be synthesised, they would have some very cool :biggrin: properties indeed.
     
  9. Jun 18, 2005 #8

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    New Scientist (like Sci Am) is not considered as an academic physics journal. They tend to either write something that has been published elsewhere, or a review, or "speculations". So do you have an exact citation on where this protonic superconductor paper was published? Unless I missed something, and unless these things are astrophysical phenomena, we have no such thing yet in condensed matter.

    Zz.
     
  10. Jun 18, 2005 #9

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Proton transport in condensed matter ? Could this be refering to hole pairs, perhaps ?
     
  11. Jun 19, 2005 #10

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    If it is, it is a very bad bastardization of the physics. Holes are not protons, as you know.

    It's one of the reasons why I dislike Sci Am and New Scientists. If one doesn't know, it's hard to distinguish which article is real, verified physics, and which one is wild speculations - and they have done the latter often. What's worse, they very seldom have exact citations. Compare this to either Physics Today or Physics World that have more accurate coverage, and certainly tons of reference materials for anyone to double check.

    Zz.
     
  12. Jun 19, 2005 #11
    It is obvious that Ns is not a journal but rather a popular magazine, it provokes discussion and interest and so I think we can forgive its many flaws - I say this as the true understanders of physics will realise the flaws within the articles, and those who are not aware of the deep physics laying behind the glosy type may be driven to learn more and be able to comprehend the article in depth - and thus realising it is flawed.

    Just my 2 cents

    -NewScientist
     
  13. Jun 19, 2005 #12

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Oh, I don't really mind the "flaws". However, I'm criticizing it from my perspective where I often have to come in afterwards and do the "cleaning up". Having been around online for a long time, I've had to correct several misconceptions and errors that people get out of such pop-sci journals and books. And to be able to do this, it helps if these articles come with a complete set of citatons they use to based the articles on.

    .. and it really is not a very good excuse that a pop-science article does not carry adequate references. Even 'glossy' articles in Physics Today and Physics World carry them. This does not distract from understanding the article for anyone not well-verse in the subject matter. Yet, anyone wishing to go into it more and look at the original source will have the ability to do so easily without going on a hunting spree.

    Zz.
     
  14. Jun 19, 2005 #13
    One may argue that on learns by asking questions - but you are right citation should be given and some of the more laughable articles should be omitted or rewritten - but all in all - I like NS!

    -NewScientist
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?