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Room Temp Superconductivity

  1. Feb 1, 2006 #1
    I will admit to first being exposed to the term "room temperature superconductivity" during a pop-sci Michio Kaku interview. However, I was wondering, just what do the scientists who actually work in the field think of the possibility of room temp sc occuring in our lifetime?
    Also, do you think we'll acheive highest Tc above 138 K this year?
    And, when will we HTS wires that aren't brittle metal oxide ceramics?
     
  2. jcsd
  3. Feb 1, 2006 #2

    Gokul43201

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    [​IMG]


    If you'd asked this question in the early 80's the answer would be, "Oh, in about 500 years, if we're really, really lucky !"...and then there was the Cuprate revolution. Now, the Tc vs time curve is leveling off again, and barring another materials revolution - the kind that you can't predict in advance - the prospects of finding a room temperature Tc in the next few decades appear low.

    The silver bullet - if there is one - may even, and this is purely speculation, turn out to be a non-cubic BCS type SC.

    PS : I do not work in the field of superconductivity. You'll have to wait to hear from Zz to get the insider scoop.
     
    Last edited: Feb 1, 2006
  4. Feb 2, 2006 #3

    ZapperZ

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    I suppose I should stick my nose in here...

    Based on what I know currently, I am skeptical of getting a "room temperature superconductor" with our present model. If there is one, it will have to be from an entirely different mechanism from the current BCS-like description.

    Strangely enough, I think the "pairing" glue might not be the major problem. The magnetic channel of coupling to form the Cooper Pairs can be strong enough to sustain pairing even at room temperature, in principle. However, as we have seen in the cuprate case, pairing does not automatically equal condensation. Unlike conventional superconductors, we have seen electrons forming pairs in high-Tc superconductors without condensing into the superconducting state (the so-called pseudogap state). These pairs can exist even up to 250K or more. However, these are incoherent pairs. They do not, for some reason, form the BE condensate that has long-range coherence.

    So there has to be something feeding the system so that a "Quantum Protectorate" kicks in. That is something I am skeptical about in getting room temperature superconductors.

    Zz.
     
  5. Mar 21, 2006 #4

    ZapperZ

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    I have a followup to this.

    Warren Pickett, a well-respected condensed matter theorist who knows this field very well, has just put out an interesting paper. In it, he outlined what we actually need in terms of the physics based on what we already know, to obtain a room temperature superconductor. In particular, he extrapolated the knowledge we obtained from MgB2, a "conventional" superconductor that, from all indications, is mediated by phonons.

    Along the way, he also gave a good short overview of strong-coupling BCS theory, something that would be necessary for something like this to occur.

    http://arxiv.org/abs/cond-mat/0603482

    Zz.
     
  6. Mar 21, 2006 #5

    Gokul43201

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    Disclaimer : This is slightly off-topic - I'm now using this thread as a place to report (and discuss) recent developments in Superconductivity.

    In a recent talk at Ohio State, Dan Shahar (Weizmann Institute) reported some of his recent work on disordered 2D superconductors. I believe the material he's studying is Indium Oxide thin films. He made two quite surprising statements - well, they were surprising to me, an outsider to Superconductivity.

    His primary result was a study of the B-field dependence of the resistivity (the magnetoresistance). At a specific value of the perpendicular field, a very interesting temperature independent resistance (=h/4e^2) was observed over a wide range of temperatures above and below Tc. He suggests that Cooper pairing is not destroyed at Tc, and persists above it, but is localized by disorder. However, this is not one of the "surprising statements" I refered to above.

    I hope I'm not distorting his results in attempting to report them :

    1. He measured the high temperature (normal phase) resistivity of the thin films, far from Tc. If I recall correctly, they displayed an exponential behavior (in T) with the activation energy given by a number very close to Tc !

    2. The second statement, though not a direct result of measurements, was quite against the grain of common knowledge as well. He suggested that in the absence of a mechanism for superconductivity, he believed that thin film Indium oxide would in fact be a metal rather than an insulator. I can't say I recall the motivation for this belief.

    http://arxiv.org/PS_cache/cond-mat/pdf/0410/0410724.pdf
     
    Last edited: Mar 21, 2006
  7. Mar 31, 2006 #6
  8. Mar 31, 2006 #7

    ZapperZ

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  9. Mar 31, 2006 #8
  10. Mar 31, 2006 #9

    Gokul43201

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  11. Apr 8, 2006 #10
    Do you think any kind of world-changing inventions -- a la the steam engine and the industrial revolution -- would come from room-temperature superconductivity? I think I saw the same Kaku interview you're talking about, and he mentioned the concept in regards to hovercrafts. But besides revolutionizing transportation and electronics -- zero resistance means no more computer fans! -- would there be a way to convert the energy in these gargantuan magnetic fields to "cheap" mechanical energy?
     
  12. Jun 8, 2006 #11
  13. Jun 8, 2006 #12

    ZapperZ

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    Since inha has bumped this thread further up, I decided to address this issue because there's a very common misconception about the usefulness of "room temperature" superconductivity if and when it is ever discovered.

    Let's look at a high-Tc superconductor having a Tc of, let's say, 100K. Now let me cool it down so that it is 90K, so it is in a superconducting state. Now how useful is it?

    First of all, the superfluid density of that superconductor depends on the ratio of 1-T/Tc. This means that at T=Tc or close to it, you have very small amount of supercurrent. To get as large of a supercurrent density, you have to go as low as you can.

    What is the implication of that? It means that at high temperatures, even in the superconducting state, the superconductor cannot carry high currents - it just doesn't have enough superconducting charge carrier for that as some point. You also can easily quench the superconductivity due to external magnetic field because there aren't that much supercurrent to provide the shielding.

    So if we come back to room-temperature superconductor, unless the value of Tc is 100K above room temperature, a room temperature superconductor is operationally useless! At room temperature, the best we can say is that it is a superconductor, that's it. To be able to do what Michio Kako imagined, it would be technically unfeasable. Even cooling it with ice would only drop it by 30K, and how significant of an advantage is that?

    In other words, room temperature or not, there is a major consideration here that is often missing in translating something into being feasible and useful. Just considering the value of Tc alone is the LEAST of such consideration.

    Zz.
     
    Last edited: Jun 9, 2006
  14. Jun 12, 2006 #13
    Thanks for the link inha. I just started reading it. So far it is quite nice.

    Nonetheless, I'd like to know what the experts on the subject of superconductivity think of the validity of some of the statements in this book.

    To quote the book, it says:

    "The main purpose of the book is twofold. First, to show that, under suitable
    conditions, superconductivity can occur above room temperature. Second, to
    present general guidelines how to synthesize a room-temperature superconductor."

    additionally, it also states:

    "In Chapter 8, it is shown that the Cooper pairs exist above room temperature in organic materials."

    These statements are news to me! Am I just learning a bunch of baloney from this book, or is this for real?
     
  15. Jun 12, 2006 #14

    ZapperZ

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    Note that, as we have seen in high-Tc superconductors,

    Pairing does not automatically implies superconductivity!

    Superconductivity requires two things to occur: (i) pairing to form composite boson AND (ii) phase coherent condensation!

    In conventional superconductors, these two occurs at almost the same temperature. In high-Tc superconductors, who knows! We see paring gap way above Tc in the normal state. Whether these pairs are the ones that will eventually form the superfluid, we don't know. We also have theories in which the formation of the pairs that will eventually condense do not occur at the same temperature as Tc. These pre-formed pairs lack the long-range coherence that is required, and will only condenses into the superconducting state at or below Tc.

    Also note the role of "geometry" here. In many materials, such as 1D organic chains, you can have pair formation, but you can never have phase coherence. This was the main criticism of the stripe model of high-Tc superconductivity. In fact, in LSCO phase diagram, when the rigid stripes actually form at one particular doping value, the material suddenly becomes normal! The stripe theory has been modified to include curly, meandering stripes scenario that allows the charge carrier to couple between stripes. This is the only way to recover superconductivity in the theory.

    There's more to superconductivity than meets the eye....

    Zz.
     
  16. Jun 12, 2006 #15

    Gokul43201

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    Alan Heeger was here last week talking about his recent work on conducting plastics. He is yet to find any superconductivity in a plastic. As Zz mentioned above, the 1D nature of the polymers poses a problem, but there is some inter-chain interaction...so Heeger believes there is a prospect for observing superconductivity. But let there be no doubt that so far, none has been found.
     
  17. Jun 13, 2006 #16
    in the case of RTc superconductors, would the superconducting band gap be larger or smaller than normal high temperature superconductors?
     
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