Talk:Superconductivity

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[edit] Inconsistency

There is an inconsistency in this article which should probably be addressed. The article states correct in the section Superconducting phase transition that the specific heat of the material varies as exp(-\alpha/T), and that this provides evidence for the energy gap in BCS theory. On the graphic to the right, the graph shows a curve with \rho \propto exp(-Δ/kT_c). As T_c is a constant (and \Delta(T) is closed to constant for T < 0.8T_c) these graph would be plotting a straight line and contradicting the text.

The graphic should be updated to read exp(-Δ/ kT) instead. (2006-10-14 Kiwidamien )

Good catch. Although I think you meant to refer to the Cv label, not ρ. Should the caption be this?: c_v \sim\ e^{-\Delta / kT} Spiel496 22:28, 15 October 2006 (UTC)

[edit] COMMENT

A long NbTi wire is achieved by joining shorter wire segments and due to joints it DOES NOT have absolutely zero electric resistance!!! It is something approx. 10E-13 Ohm/cm when superconductive. In addition in a superconductive magnet system, the joints for the superconducting switch also influence the resistance. When you put current for the first time in the superconductive coil, the normal conductur has to be attached somewhere to the superconductor. This joint is the most critical part of a magnet. In a typical magnet the coil is several thousand meters of NbTi wire (eg. in a 4.7T Oxford NMR magnet the length of the wire of the coil is = 27 km) there is measurable current change / B-field change, called natural decay. This can be measured by looking at cyclotron frequencies of ions in a Penning trap placed in the magnetic field generated by the superconductor. Due to natural decay, this cyclotron frequency (which depends linearly on the magnetic field) decreases e.g. by 1 part in 10E9 in an hour.

[edit] Just a question

Okay, if volts/amps = resistance, and a superconductor has zero resistance, then the amps must be infinite, correct? Also, because watts = volts*amps, wouldn't that mean there would be infinite watts flowing through the superconductor? I'm sure theres some sort of quantum limit to the amount of amps that can flow through something, but could anyone clear this confusion up for me? Thanks in advance. --Bejitunksu 06:46, 5 July 2006 (UTC)

The missing piece is that because a superconductor's resistance (to DC) is effectively zero, when you apply any finite current, you don't have a voltage drop across the superconductor. Power dissipated in the superconductor is zero (for a DC current) because of this. In practice you get two things happening to give you nonzero power dissipation. First, your power supply isn't superconducting. It dissipates power in its own internal resistances (this is why batteries get warm when under heavy load, for instance). Second, the superconductor still has inductance. This means that to _change_ the current, you have to put in (or take out) energy that corresponds to the change in the amount of energy stored in the magnetic field around the superconductor. When the current is changing, the superconductor has a voltage across it (like any other inductor). The power dissipation for this case is finite, and any energy put in can be taken out again (or at least, isn't lost in the superconductor, though non-superconducting parts of the equipment may have losses). All of this applies at DC or nearly-DC. If you have a quickly changing voltage or current, other forms of loss occur within the superconductor (it isn't an ideal conductor for AC). I hope this explanation is useful to you. --Christopher Thomas 07:03, 5 July 2006 (UTC)

Another question: Why does this work? I'm talking about the movement of the electrons, not math. I need help, would you please help me?

[edit] Junk at the top

I'm sure cobalt oxides are interesting research, but it's far too obscure a topic to be in the intro. Perhaps this class of materials could be mentioned in a section on exotic superconductors. Spiel496 15:08, 21 May 2006 (UTC)

I would like to see some information on the nuclear resonnance properties of type II superconductors. If electromagnetic radiation is applied to the superconductor at its main resonnance frequency will the radiation be deflected or absorbed? --cacapitol

Somewhere we need to mention the specific temperatures for some superconductors - and note that high temperature is not high in normal life. Probably need to use Celsius, not Kelvin scale for general readers. --rmhermen

It would be ridiculous to use any non-absolute temperature scale while talking about superconductivity. We would end up saying things like "X degrees Celsius above absolute zero." By the way, I am a general reader when it comes to superconductivity (or physics in general). -- 130.94.162.61 13:38, 15 January 2006 (UTC)
However, it would be nice to provide a link to another article that explains the relationship between various temperature scales, including Kelvin, Celsius, and Fahrenheit. A conversion table for low temperatures might be nice in this article, just to give the general reader an idea of how cold these temperatures really are. -- 130.94.162.61 13:48, 15 January 2006 (UTC)

I have re-written the article so that the distinction between conventional superconductors and unconventional superconductors is made clear. This is important, because although the field of unconventional superconductivity (including high-temperature superconductors) is very ebullient, conventional superconductivity on the other hand is a very well-established subfield of solid-state physics (and particularly BCS theory is a fully-working theory, if you apply it to conventional superconductors). But the article seemed to have more about unconventional superconductors than conventional ones, which is odd. I have not deleted that material, but moved it to new articles (unconventional superconductors, high-temperature superconductors, technological applications of superconductivity). Hope this is all right.

By the way, I think keeping the Kelvin is all right, since it is the natural unit in superconductivity. It is important to have links to its definition, though. --quintanilla

It is good that you decided to keep it in Kelvin considering that it is the SI unit for physics. --west

I'm a bit in doubt about the first line. I'm not sure superconductivity is a "state of matter", but a characteristic of certain elements and substances in given conditions.

--

We know that superconductivity is not a property of metals, but a thermodynamic state of matter different from the metallic state, because of the Meissner effect. The argument is quite standard: a perfect metal (i.e. one with zero resistivity) would support resistanceless flow of an electric current and expel magnetic fields from its interior, just like a superconductor, but if at high temperatures, when the resistivity is finite, a magnetic field is applied, and then the temperature is lowered, the perfect metal does not expel the field, while the superconductor does. In contrast superconductivity is really a thermodynamic state which is characterised by zero field inside the sample however you got there (applying field first, cooling down afterwards, or the other way around). I know this is very sketchy. When I have time I will write it more carefully in the articler about the Meissner effect. Or if you have more time than me maybe you can look it up in "Superconductivity", J.B. Ketterson and S.N. Song, Cambridge University Press 1999, Section 1 - Introduction (pages 1 and 2) or in any other textbook on Superconductivity (e.g. the one by Tinkham, or the one by Schrieffer). Since this argument usually appears in the introduction of such textbooks, it is usually written in a way that is relatively easy to understand. Ciao, jqt

Why change "External links" to "Web resources"? The former is more common in wikipedia? Tiles 08:06, 29 Jul 2003 (UTC)

I'm very curious what energies have been achieved in superconductors, as a novice. I have heard rumours that superconductors have potential applications as energy storage devices. --dikaiopolis

Currently it says Superconductivity was discovered in 1911 by Onnes. This is somewhat disputed and it is more diplomatic to write Onnes was awarded the Nobel Prize for discovering superconductivity in 1911. I have not rewritten it yet, awaiting more comments before doing so.

Any references? -- CYD

This is known within the superconductivity research community, which is where I picked it up. As with much dirty linen it is not washed in public, thus the rewrite proposal that Onnes got the Nobel prize for it in 1913 (which is undisputed) for the discovery made in 1911 (which is where the controversy lies). A number of Nobel Prize laureates have turned out to be under some controversy. Very, very little of this can be found on the net, one example is the omission of Bell for discovering pulsars. You could make a Wikipedia entry for this alone, that is if you wanted the mother of all edit wars; there is a lot of prestige at stake. Thus I propose Onnes was awarded the Nobel Prize in 1913 for the discovery of superconductivity in 1911.

Might do better to del any ref 1911, N? I've seen him cred with it that yr, & this's first mention of controversy over it I've seen (tho I'm no superconductivity splst...) Trekphiler 18:35, 6 December 2005 (UTC)

[edit] Tesla / Superconductor myths

I deleted reference to Tesla. The patent mentions the well known fact that resistance increases with temperature. The patent talks about reducing the resistance by cooling, but no mention of zero resistance. He discusses metallic conductors and liquid air cooling. Even today, there is no metallic conductor which is superconducting in liquid air. pstudier 23:05, 2005 Jan 24 (UTC)

The patent mentioned is:

  • Tesla, Nikola, 685,012, "Means for Increasing the Intensity of Electrical Oscillations". 1900 March 21. USPTO.

pstudier 23:13, 2005 Jan 24 (UTC)

See classications @ http://www.uspto.gov/go/classification/ of US patent 685,012. The patent current U.S. Class is classified as :

Class 327 MISCELLANEOUS ACTIVE ELECTRICAL NONLINEAR DEVICES, CIRCUITS, AND SYSTEMS
527 Superconductive (e.g., cryogenic, etc.) device
Class 505 SUPERCONDUCTOR TECHNOLOGY: APPARATUS, MATERIAL, PROCESS
888 Refrigeration
870 Power supply, regulation, or energy storage system : Including transformer or inductor
856 Electrical transmission or interconnection system

This is besides the mention of the recent US patent citation of US4869598.

Does it matter how the patent office classifies the patent? It should be important. Does wikipedia just deny the facts? I hope not. This patnet does describe the process that would result in superconductivity.

Sign your edits! I have read that whole patent and NOWHERE included in it does Tesla mention any phenomena which describe anything other than the already widely known effect of ordinary reduction of resistivity with the lowering of temperature. It does NOT describe the observation of any superconductive phenomenon. Who cares if the clueless patent officer doesn't know the difference between mere cryogenic conditions and those of superconductivity! Jeez who knew there were so many fawning hyper-obsessive Tesla fanboys here. STOP ADDING this inconsequential, unrelated, nothing edit to the article!--Deglr6328 18:58, 12 Mar 2005 (UTC)
Deglr6328, "Fanboy" that is not NPOV!
The patent office classifies the patent as superconductivity tech (that is important). The patent suggests superconductivity.
The process patented is to increase the ability to keep current (as Onnes himself verified in 1912).
It does describe "zero resistance" .. read the patent, Page 2, lines 50 - 85.
The theory necessary for superconductivity was established by Dewar and Flemming. Tesla understood this and was using Linde's machines [the same thing that Onnes himself used and modified]. Tesla had best equipped lab in the world (from the vast amount of money he made from Westinghouse; and he had many wealthy financiers backing him).
Tesla achieving this, not in secret (read his notes written in colorado springs), with prior knowledge on super-cooling (he had a physics degree and was widely known in europe and america by the best scientists (note who is in his quotation section)). The theory of superconductivity was established nearly a decade earlier than Onnes (again, Dewar and Flemming set forward the notion!).
The superconductor is not an oscillator, but the particular winding of the coil sets up the oscillations. (But you'd have to understand coils (like the bifilar that Tesla invented), each have a specific resonance and frequency, to grasp that!)
The above Page 2, lines 50 - 85 is about operation of the apparatus. You can read the following to get a better idea: Page 1, lines 25 to 39 (best results method). Page 1, 62 to 78 (previous experiments, discovery of circuit to vibrate freely). Page 1, 79 to 83 ("extraordinary degree magnified and prolonged"). Page 2, 3 to 12 (agents used and how-to construct). There is alos the claims, the fifth one is interesting to this discussion


Also read the discussion at Talk:List of Tesla patents. Same Tesla nonsense going on there also. pstudier 19:15, 2005 Mar 12 (UTC)

Is this true? Additionally, melanin is an organic, polymeric superconductor currently in use in bio-tech research as a possible replacement for gallium arsenide and silicon in high-tech devices -- most notably in nanotechnology and plastic electronics applications. What is its critical temperature? 69.225.131.186 00:53, 6 Feb 2005 (UTC)


You're right. The three edits by Deeceevoice were vandalism. I have reverted them. Thank you for catching that. RJFJR 01:48, Feb 6, 2005 (UTC)

(The prior statement that the edits were vandalism may have been unnecessarily strong; however, the contention that melanin is a superconductor is not supported by mainstream science and does not belong in this article. RJFJR 02:11, Feb 6, 2005 (UTC) )

I do not engage in vandalism. I have reinserted the passage -- but placed it in a previous paragraph that refers to unconventional superconductors. Please don't speak/write on matters about which you know nothing. Use your computer's search engine and investigate before making groundless charges. No one can know everything. [I believe the winners of the 2000(?) Nobel Prize in science were engaged in this kind of research.] There are numerous biotech companies currently engaged in melanin research. What is with you folks, anyway? If melanin were ketchup (or any other organic substance) and not associated with black folks, and if I were not black, would you have been so quick to assume "vandalism"? Very telling. Ya better take a couple of steps back and check yourselves.deeceevoice 03:43, 6 Feb 2005 (UTC)

OK, not knowing anything about that, I'm leaving that alone, but I cut out the link to black supremacy because the connection between superconductivity and black supremacy is really tenuous. - furrykef (Talk at me) 04:34, 6 Feb 2005 (UTC)

No, melanin is not a superconductor. Curiously enough, when I used "my computer's search engine", I came up with this. -- CYD

I'm not finding any claims that melanin is a superconductor except in reference to claims of black supremacists... if it really were a superconductor I don't think people would be hush-hush about it (because, quite frankly, I don't think that would provide any real benefit anyway... and Hell, we already know that extra melanin is good to have because it prevents sunburn and skin disease, so it's not like we're keeping benefits of melanin a secret). - furrykef (Talk at me) 04:50, 6 Feb 2005 (UTC)

Go to http://nobelprize.org and search on melanin. The only mention's are in the medicine prizes and concern its biological role. The 2003 physics prize was about superconductivity theory with no mention of melanin. The 2000 chemistry prize was for conductive polymers, no mention of either superconductivity or melanin. Can anyone cite any evidence for melanin being either a conductor or a superconductor? pstudier 05:49, 2005 Feb 6 (UTC)

My profoundest apologies. My edits to Superconductor were the result of an inexplicable cognitive trip (of the really stupid sort that people often make while typing and composing at the same time). The Melanin Theory holds that melanin is a superconductor, when it is widely known to be a semiconductor. This is commonly known in the scientific community (even in its more mundane areas of application such as dermatology and cosmetics with regard to sunburn/melanoma prevention) -- which is why, in reading your comments about my edits, I took such exception to your reactions. I simply didn't understand them.) In editing Black supremacy, I thought to mention the subject of MT and so included it. I explained that MT holds that melanin is a superconductor, but when I went on to explain its recognized physical properties, I inadvertently continued to use "superconductor," when I intended to switch to the appropriate "semiconductor" in its stead. I will allow the reverts of my edits to superconductor because they certainly were not what I intended. I have also made the appropriate changes in related articles, with an added "erroneously" in Black supremacy, where this all started, to emphasize the difference between "superconductor" and "semiconductor."
Come to think of it, I will have to see if black supremacist theory actually recognizes the difference -- that melanin is, in fact, a semiconductor; and if the notion of it being a superconductor is just a misnomer and a distortion of information by the ill-informed that occurred over time. If so, I'll have to go back and correct that, as well. deeceevoice 11:44, 6 Feb 2005 (UTC)
I've added a lot of information to melanin regarding its properties as a semiconductor. You may want to visit and read up. (I think if you were familiar with this subject, you might have caught my earlier slip. Sorry -- again.) The 2000 Nobel Prize in Chemistry was, indeed, awarded to three scientists involved in research into melanin as a polymeric semiconductor. deeceevoice 13:19, 7 Feb 2005 (UTC)
And, FYI, the earliest research (with which I'm familiar, at least) on the semiconductivity of melanin was published in 1974. The related Melanin Theory has been around since about that time and brought this knowledge of the scientific research to members of the African American community 30 years ago. deeceevoice 15:37, 7 Feb 2005 (UTC)

[edit] Perfect diamagnetism

"The Meissner effect is distinct from perfect diamagnetism because a superconductor expels all magnetic fields, not just those that are changing."

As I read this line from this Wikipedia article, I am also reading this paragraph from my copy of Serway and Jewett's "Physics for Scientists and Engineers with Modern Physics 6th Ed." textbook:

"The Meissner effect is illustrated in Figure 43.34 for a superconducting material in the shape of a long cylinder. Note that the field penetrates the cylinder when its temperature is greater than Tc [the critical temperature]. As the temperature is lowered to below Tc, however, the field lines are spontaneously expelled from the interior of the superconductor. Thus, a superconductor is more than a perfect conductor (resistivity ρ = 0); it is also a perfect diamagnet (B = 0)."

To me, it seems like whoever wrote the Wikipedia article was implying that the Meissner effect has nothing to do with perfect diamagnetism, thus, implying that superconductors are not perfect diamagnets; on the other hand, Serway & Jewett seem to imply that the Meissner effect occurs because superconductors are perfect diamagnets. Can anyone explain this apparent contradiction to me? RTL 03:08, 20 July 2005 (UTC)

The answer is that Serway and Jewett are wrong. A perfect diamagnet can only cancel out any change in the applied magnetic field. It cannot expel an existing magnetic field, unlike a superconductor. -- CYD
Many thanks, I appreciate it. I'll scribble that in my textbook margin :) RTL 06:38, 7 August 2005 (UTC)

Actually, Serway and Jewett are right. The Meissner effect is synonymous with perfect diamagnetism. What they explain is that infinite conductivity doesn't imply perfect diamagnetism and thus that both properties are important characteristics of superconductors. _R_ 16:56, 3 September 2005 (UTC)

Depends on what you mean by "perfect diamagnetism". It's probably better to avoid this ambiguous term. -- CYD
Since "diamagnetism" means "tendency to expel magnetic flux", "perfect diamagnetism" means "complete expulsion of magnetic flux". I don't see how it's ambiguous. _R_ 02:21, 20 September 2005 (UTC)

The articles Meissner effect and Superdiamagnetism are almost entirely inferior versions of material here. Does anyone else think they should be merged into Superconductivity? I'll do it myself eventually. --newbie

They definitely ought to be merged. But I'm not sure they ought to be merged into this article: it's easier to link to Meissner effect than to Superconductivity#Meissner effect. _R_ 02:21, 20 September 2005 (UTC)

[edit] Open up a little

Lossen up, Superconductivity is not only levitating magnets. It's used in particle accelerators too in a different manner. It's in a vacuum and you can get better results when you drop the temps and introduce a particle beam, So open up a little...

Hope you get to see the picture at *SNS before it goes away. Scotty


[edit] Podkletnov "Gravity Shield"

I know the Tampere Gravity Shield has been largely discounted, but still, some metnion of the phenomenon should be noted here, no? I really don't know enough about the subject to write about it, but, from what I understand, the acceleration due to Earth's gravity decreases by ~3% above a rapidly spinning superconducting disk. - ZelmersZoetrop

[edit] Classical superconductors

I took the liberty of adding a sentence at the top of the article distinguishing real superconductors from classical superconductors -- this is a perennial source of confusion among physics students who have learned about resistivity but not about Cooper pairs. If folks find it problematic, please feel free to move it down to a section somewhere. zowie 18:01, 7 September 2005 (UTC)

It's fine, except that I've never seen the expression "classical superconductor" used in that sense. It seems to me that it's actually a less common synonym to "conventional superconductor". I replaced it everywhere by "perfect conductor", which is commonly used and unambiguous. _R_ 02:28, 20 September 2005 (UTC)
Actually, that rephrase misses the point. Both classical superconductors and real superconductors are perfect conductors; the concept of a classical superconductor is a useful contrast to the strange phenomenon that is real superconductivity. Although the more sloppy usage has become vogue, it is arguably incorrect ("classical" is most commonly used in physics contexts to mean "non-quantum"). Perhaps that calls for a disambiguation article. zowie 19:35, 21 September 2005 (UTC)

[edit] Unified theory?

If superconductivity is a phase of thermodyn, as suggested, it implies to me a connection between EM & thermodyn, a "unified field theory" of a sort. Or am I blowing it out my stern? Trekphiler 18:38, 6 December 2005 (UTC)

Um, IIRC the phrase "unified field theory" usually describes a unification of fundamental forces, especially the historical case of Einstein attempting to unify EM and gravity. Since thermodynamics isn't a fundamental force, its interaction with EM probably ought to be called something else, even when it is manefested in a field theory. I'm afraid I don't have any real insights into the connection, though. Melchoir 19:31, 6 December 2005 (UTC)

[edit] necessarily low temperatures?

IIRC. although low temperatures seem to be a requirement for phase transition for superconductivity, it seems like a relative kind of thing ie. compared to that substance's boiling and melting points rather than say, "cold or hot" per se. Ideally, we want to discover substance that has superconductivity at relatively high temperatures...so we could use them in nuclear fushion for example. Not quite concrete, but not fantasy either. Would definition need adjustment for exception? -- Natalinasmpf 21:21, 7 December 2005 (UTC)

Well, a more precise intro would say "Superconductivity is a phenomenon occurring in certain materials at sufficiently low temperatures". Even if we discover/synthesize room-temperature superconductors, superconductivity is still a phenomenon that takes place below some critical temperature, and not above. It also happens that all known superconductors have critical temperatures lower than everyday experience, so the word "low" is kind of doing double duty. For now, it's fine. Melchoir 22:02, 7 December 2005 (UTC)

[edit] Did someone delete two image files associated with this article?

Image:Superconducting-transition.png and Image:Superconductor-b-vs-h.png are both missing. What's going on? —The preceding unsigned comment was added by Peter bertok (talk • contribs) on 04:25, 20 December 2005.

I can confirm that they were once present, but it apparently requires admin privileges to see the history for deleted pages. Most likely reason was that they couldn't be verified to be under an acceptible license (copying textbook figures for this article wouldn't be "fair use"). For the actual reason, wait until an admin notices the thread, or painstakingly search for it under WP:IFD.--Christopher Thomas 20:06, 29 December 2005 (UTC)

I'm an admin and stubled across this. Here's the info from the deletion logs... --Samuel Wantman 08:53, 15 January 2006 (UTC)

[edit] Deletion log Image:Superconducting-transition.png

  • 09:29, 10 December 2005 JesseW deleted "Image:Superconducting-transition.png" (WP:CSD Image #4 - "Images in category "Images with unknown source" or "Images with unknown copyright status"which have been on the site for more than 7 days, regardless of when uploaded.")
  • 09:29, 10 December 2005 JesseW deleted "Image:Superconducting-transition.png" (Deleted old revision 20030715072604!Superconducting-transition.png.)

Page history

  • 23:19, 10 January 2005 . . RedWolf ({{unverified}})
  • 12:05, 14 July 2003 . . CYD (superconducting phase transition diagram)

[edit] Deletion log Image:Superconductor-b-vs-h.png

  • 09:29, 10 December 2005 JesseW deleted "Image:Superconductor-b-vs-h.png" (WP:CSD Image #4 - "Images in category "Images with unknown source" or "Images with unknown copyright status"which have been on the site for more than 7 days, regardless of when uploaded.")

Page history

  • 23:19, 10 January 2005 . . RedWolf ({{unverified}})
  • 11:55, 26 July 2003 . . CYD (B vs H curves for Type I and II superconductors)

[edit] zero resistance?

I was wondering about what exactly zero resistance means. Usually, the lower the resistance of an element in a circuit, the higher the current through it will be, increasing toward infinity. If superconductors truely have zero resistance, the does this mean that the current through it is only limited by the resistance and current capacity of the source of voltage? I would expect that even superconductors have a very tiny resistance (if they didn't, then why would larger currents heat up the superconductor?). It seems like "zero resistance" means "unmeasureable resistance, but theoretically still there. Fresheneesz 03:28, 30 May 2006 (UTC)

The resistance really is zero. I think the article muddles this point a bit, and maybe I'll rewrite the section after I make sure this hasn't been argued about before. The article states that the "easiest way" to measure the resistance is to place a voltage across the sample and measure the current. So, you're looking to measure an infinite current?? That doesn't sound "easy" to me, and that's not how it's done in practice. It's much clearer to describe what is done in practice. You pass a current through the sample and measure the voltage across it. If it's a superconductor, the voltage will be zero, by V = I*R. Using separate contacts for the voltage measurement, you can eliminate the effect of contact resistance, but that is probably unnecessary detail. Spiel496 18:12, 20 June 2006 (UTC)

Yup, in normal use the current through a superconductor is only limited by the resistence and/or current capacity of its supply. In practice, there is a limiting current density above which the material stops being a superconductor -- but below that, yup, there's zero resistance. The easiest way to demonstrate that is to notice that L/R yields a time constant for circuits with both an inductor and a resistor in series. Since every circuit element has some inductance to it, if you momentarily induce a current in any closed passive circuit (like a loop of wire) there will be a decay time before that current dissipates. If the wire happens to be made of a superconductor, it will *never* dissipate until some external system interferes with the circuit -- R is zero, so the decay time L/R is infinite. zowie 03:55, 30 May 2006 (UTC)

How would one measure that the current doesn't dissipate? I suppose if you let it sit there, and then connect a multimeter looking for a blip... It just makes more sense to me that the resistance is tiny, but not 0. Fresheneesz 05:31, 30 May 2006 (UTC)
From its induced magnetic field. A ring of superconductor carrying a current is effectively a permanent magnet. zowie 13:20, 30 May 2006 (UTC)

"theoretical estimates for the lifetime of persistent current exceed the lifetime of the universe."

The universe does not have a defined lifetime, and is expected to expand forever. This could be changed to say "...exceed the amount of time the universe has been in existence", but I do not know what the original author was trying to say. No citation is given.


[edit] Superconductors and ac

Do they go together?--Light current 22:45, 26 June 2006 (UTC)

Short answer is "no". In addition to the impedence you get from any wire's inductance, my understanding is that you also get the flux vortices moving around under AC conditions, which causes losses. Not sure what the equivalent is for Type I superconductors, but my understanding is that some similar mechanism causes (very small) resistance. --Christopher Thomas 22:51, 26 June 2006 (UTC)
Actually there are some interesting developments with detectors which apply an ac voltage across a superconductor at its critical temperature, to detect tiny changes in temperature (due to incident particles) by the change in resistance. They're called Transition Edge Sensors, and are used in CDMS (though that project may use a dc voltage, I'm not sure) --AlmostReadytoFly 21:33, 25 July 2006 (UTC)


[edit] Superconductors and space

In space, the temperature is zero, right? So wouldn't space-travel related superconductors work fine in space, because there is no temperature in the vacuum? --01:13, 31 July 2006

Not quite. First of all, space isn't a perfect vacuum, and even if it were, things in space are still heated by radiation. For human-launched missions, that means sunlight. Melchoir 01:34, 31 July 2006 (UTC)

[edit] History Section Misses an Important Player

I was told by a Physics professor than Onnes was NOT the discoverer of superconductivity. It was one of his graduate students. And Onnes refused to share any credit. I am having a difficult time tracking down the name of this student, but the previous link may be a clue. --Bex 01:15, 1 August 2006 (UTC)

[edit] Power Applications of Superconductivity

This article, like many others, promotes the idea that superconductors could revolutize electric power applications like tranmission, machinery, and transformers. I agree that a zero-resistance conductor would reduce losses in these applications, but I disagree that superconductors are likely to see widespread use in such applications (at least in the foreseeable future).

Regarding power transmission lines, very little of the grid loss occurs during transmission, which is 98% to 99% efficient across even very long distances. Yes, improving this would save "millions" of dollars, but only with incredibly high investment on a financial scale that is in the billions. Further, widescale change to different conductor is also impractical, even if superconductors were somehow free, reliable, mechanically strong, and had very high critical temperatures. Very little transmission has been built in the last two decades due to siting conflicts and legal battles. Further, power generation is moving toward more distributed, rather than centralized, architecture. Consider solar-electric generation, for example, which can be placed on rooftops. In developing countries with no infrastructure, distributed generation would likely be very common, with little need for long transmission.

Consider that some superconductor transmission proposals involve hydrogen "supergrid" ideas. Such ideas involve piping liquid hydrogen everywhere. In the pipes, we would use superconductors to transmit electrical energy. The hydrogen would be used to power fuel cells. This is even less practical than replacing existing transmission, with similarly little benefit. Compare this to simply using the liquid hydrogen (or whatever) for cooling copper by 120 K, which would roughly cut the resistance in half. This would roughly halve the losses without using superconductors at all! However, generally speaking, I would be in favor of more DC transmission for reasons beyond the scope of this discussion.

Regarding transformers, there are, as mentioned, many technical difficulties in implementation. The difficult mainly lies in the AC nature of transformers. However, I would also argue against the need for such a device. Like transmission, very little loss occurs here. There is a huge installed infrastructure of high efficiency, high reliability, transformers based on very inexpensive steel and copper. By the time that an AC superconducting transformer could be invented and be anywhere near cheap enough to compete, I would argue that there would be no need at all for such a device. Transformers are needed to step-up voltage of low-current transmission, but if we had superconducting transmission (which I don't think we will) there would be no need to transmit at low current. There are already many advances being made on electronic transformers that would offer many benefits over conventional transformers. Such devices are far more practical than any superconducting technology, yet still are considered too unreliable and too expensive today. Finally, as above, as power generation becomes more distributed, it is hard to see where highly efficient transformers have significant advantage.

Consider that even with steel and copper, much of the loss is in the magnetic core, not in the wire. A superconducting transformer would presumably not use a magnetic core, but in that case the flux would not be contained to a small area, potentially causing interference with nearby electronic devices. If a conventional steel and copper transformer is 99% efficient at full load, and that is somehow not good enough, then we need only make the thing twice as big (roughly) to halve the losses. This would make the transformer about 99.5% efficient, for "only" double the cost with no technology revolution at all. Compare this to the huge cost of researching, developing, and manufacturing superconducting transformers which would only save about 1% of the power transmitted.

Widespread use of superconductors in motors and generators is similarly flawed. Few machines use DC current. Synchronous generators do in their field winding, but this is only part of the total loss. Such experiments have shown improvements in efficiency but at debatable payoff considering the cost of cryogenics and decreased reliability. Even so, affordable generators with permanent-magnet rotors already eliminate conductor losses, and are now quite common. As stated, future power generation will rely more on distributed, renewable resources like solar power or fuel cells. Superconducting generators could be used in wind-power systems, but again, conductor losses are only a small part of the total loss and hardly worth much additional cost.

There already exist many ways to make motors more efficient, but they are not used in nearly every motor because they cost more. The whole motor industry is obsessed with cost and cares little about efficiency. Only in specialty applications, but increasingly so in an "EnergyStar" sense does efficiency take precedence over cost. In high power applications, motors already have efficiency in the upper 90s. Like transformers, we can make them more efficient by making them bigger. Superconductors would only offer an advantage if weight is a major factor, such as in space or aerospace applications.

To summarize, the power applications of superconductors are problems that have already been solved. True, superconducting versions would be better in some ways, but also cost much more and have reliability concerns. This is a "do more with more money" engineering approach, which seldom wins in the market. If superconductors can somehow be cheaper and more efficient than copper, while offering no sacrifice in temperature (e.g. RTS), mechanical strength, or reliability, then they would be worth consideration. This would be a "do more with less money" approach, which is a market winner, but hardly seems likely. It is my opinion that few of the superconductors researchers really know anything at all about the applications, such as power applications, they promise to revolutionize. Only in the very distant future, when humanity's needs and challenges hardly can be predicted and the needed advances in physics have been made, might superconductors play a widespread role in such applications.


[edit] GA Re-Review and In-line citations

Members of the Wikipedia:WikiProject Good articles are in the process of doing a re-review of current Good Article listings to ensure compliance with the standards of the Good Article Criteria. (Discussion of the changes and re-review can be found here). A significant change to the GA criteria is the mandatory use of some sort of in-line citation (In accordance to WP:CITE) to be used in order for an article to pass the verification and reference criteria. Currently this article does not include in-line citations. It is recommended that the article's editors take a look at the inclusion of in-line citations as well as how the article stacks up against the rest of the Good Article criteria. GA reviewers will give you at least a week's time from the date of this notice to work on the in-line citations before doing a full re-review and deciding if the article still merits being considered a Good Article or would need to be de-listed. If you have any questions, please don't hesitate to contact us on the Good Article project talk page or you may contact me personally. On behalf of the Good Articles Project, I want to thank you for all the time and effort that you have put into working on this article and improving the overall quality of the Wikipedia project. Agne 00:07, 26 September 2006 (UTC)

[edit] Disorder Field Theory

I admit I'm just an experimentalist, but the statement added 2006-09-29 goes way over my head: "The Lambda transition can also be understood as a consequence of the proliferation of vortex lines in such systems. A theoretical description of superconductors and superfluids in terms of their vortex lines is known as disorder field theory." Is this really about superconductivity? Can someone explain why it belongs? Spiel496 03:54, 30 September 2006 (UTC)

I guess the answer is "no"; sentence deleted. Spiel496 17:24, 4 October 2006 (UTC)
Just to answer the original question. Each vortex line carries with them an area of normal state material (the area has the radius of about a healing length). One interpretation of the normal-superconducting phase transition is that by adding more and more vortices, eventually, the entire sample is now in the normal state. —The preceding unsigned comment was added by 18.19.5.150 (talk) 18:34, 12 February 2007 (UTC).

[edit] List of Superconductive Materials already mentioned in Wikipedia

Niobium, Niobium-titanium, Niobium-tin, Niobium nitride, Rhenium, Rhenium-tungsten, Rhenium-molybdenum, Zirconium, Gadolinium, Ruthenium, Protactinium, Tin, Technetium, Aluminum, Magnesium diboride, Strontium titanate, Yttrium barium copper oxide, Bismuth strontium calcium copper oxide, Boron-doped diamond, Vanadium, Vanadium-gallium.

Superconductivity not mentioned: Indium, Lanthanum, Indium-telluride, Lead, Mercury, Wood's metal, Rose's Metal

[edit] How to remove an "improper" sentence?

Someone wrote:

Also if you have sex with out a condom you can get AIDS

in the article, in the "Zero electrical DC resistance" section. Can someone remove it? —The preceding unsigned comment was added by 130.237.20.183 (talk) 10:32, 8 February 2007 (UTC).

A. Sign your posts. Use 4 tildes, ~~~~

B. You could edit the page, use the little edit link at the top of the section. C. If it dosen't show up you have a problem, dunno how to fix it... D. Problem has been fixed. 64.198.215.3 19:31, 11 February 2007 (UTC)

[edit] Mistaken new user edit, hiding IP in history

Is it possible to hide my IP and the subsequent UNDO in the history? I've never edited a wiki article and was showing a family member how wonderful Wikipedia is, and apparently it's even faster to make an edit than I thought. Now I have a user-id, but don't know how to get rid of the public visibility of my past-edit's IP.

Thank you.

SeaProgrammer 17:54, 19 February 2007 (UTC)

[edit] Obscure References

I note that there are two references to some obscure papers by Kleinert. I have not looked them up, but I am quite certain that they are not really relevant to informing anyone about the subject of superconductivity. Properly, research articles should not be referenced unless they present important and relevant results.

[edit] Is this line correct?

It cannot be understood simply as the idealization of "perfect conductivity" in classical physics.

Or should it be:

It can be understood simply as the idealization of "perfect conductivity" in classical physics.

Themania 08:07, 18 March 2007 (UTC)

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