Talk:Superconductivity

critical field and current density

I'm not sure how to do it but i think the article needs more on the critical field(s) (Hc) and critical currrent density (Jc) of SC as these greatly affect the potential use of SC materials. A table of Tc, Hc, Jc for various SC might be useful here. Even a diagram of Tc v Hc with curves for various SC. Rod57 (talk) 16:05, 3 June 2008 (UTC)

Question

.. to somebody being familiar with superconducting physics: Would it be possible to gain energy out of a magnetic field like Earth's field by a switchable superconductor?

Suppose, a superconducting disk is placed near a coil, and the superconductor would be very small (say, 1mK) above its transition temperature. So, the external magnetic field (for instance Earth's field) would be able to penetrate that disk. Now, the disk is cooled to remaining 1mK and becomes superconducting. Then, it is perfectly diamagnetic and expells the external field. Thus, the field lines now will be inhomogeneously around the disk, so a change dB/dt<>0 occurs, resulting in a voltage and current pulse at the surrounding coil.

Now, an induction could be achieved also, when the superconductor in its superconduction state is heated 1mK above its transition temperature. Then, the external magnetic field would be penetrating again the disk, and the inhomogeneously concentrated field lines would no longer be concentrated at the coil. So, at the moment of reaching the transition temperature, there would be again a dB/dt<>0 and an induction impulse at the coil.

That there is an induction at the coil would be independently, whether cooling down the disk below transition temperature or heating it up above that temperature. It would work in both directions, and even fully reversible (as superconductors are). The magnitude of the induced voltage pulse would be dependent only on the geometrical size of the disk and the external magnetic field, but not on the actual value of the transition temperature or the temperature change.

So, therefore, the question arises, where the energy at the coil is originated? Is it converted from the external magnetic field (like a reverse electric magnet)? From my viewpoint, it could not come from the heating/cooling of the superconducting disk, as one could place that disk also in an environment (like on a satellite or in outer space), where naturally low temperatures exist. Also, the formulas concerning the induction in the coil, would have no thermodynamic terms.

An apparatus converting permanently energy from Earths magnetic field would thus be very simple: Just place a superconducting disk at an holder in a bath of liquid nitrogen, and a coil around that disk, and then let the disk mechanically be moved by a electric clapper in and out the LN2, synchronized by the voltage output of the coil, thus having periodic cooling and heating below or above transition temperature.

It could be even done without changing the temperature, i.e. iso-thermal, by choosing a superconductor having a critical magnetic field of, say, 95% the applied external magnetic field. Then, an additional alternative magnetic field (5%) is added by a second coil to that field, so that at the positive superposition the superconductor becomes normal-conduction, and otherwise is superconducting. Because of the expelling of the total magnetic field out of the superconducter (ideal diamagnet), the full field would originate the induction pulse at the first coil (100%).

Could you tell me your opinion about that thought experiment?

Indefinate flowing current?

'An electrical current flowing in a loop of superconducting wire can persist indefinitely with no power source.' I was under the impression that a current in a superconductor would not persist for ever. "The decay of supercurrents in a solenoid was studied by File and Mills using precision magnetic resonance methods to measure the magnetic field associated with the supercurrent. They concluded that the decay time of the supercurrent is not less then 100 000 years." From 'Introduction to solid state physics' C. Kittel (Wiley, 1996). Which is true the article or the above quote or are they both true and I've misinterpreted something. -- 137.222.14.123

I'm probably the source of that vague word "indefinitey". I didn't want to say something like "forever" or "100,000 years" because that has no practical meaning. Long before 100,000 years goes by, something else is going to stop the current -- loss of coolant, meteors, funding cuts, you name it. In the intro, we just want to make the point that the decay time of the current is longer than every other timescale a human is going to care about. Later in the article, yes, that would be interesting to point out the measurements of decay. Does anyone know more about this kind of experiment? I suspect decay is seen only in Type II superconductors. Spiel496 17:52, 17 April 2007 (UTC)

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 $C_{v}$ label, not ρ. Should the caption be this?: $c_{v}\sim \ e^{-\Delta /kT}$ Spiel496 22:28, 15 October 2006 (UTC)

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.

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?

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)

Of course Kelvin notation can be translated into Celsius or Fahrenheit notation -- any online temperature conversion applet can do it. Zero degrees degrees Kelvin equals -273.1500000 degrees Celsius. Professor Muller at UC Berkeley provides this information in his online courses -- just Google "pffp" and you will find about the most accessible explanation of superconductivity on the Internet.

---

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)

The first publication on superconductivity by Onnes was in 1911 - Ref. H. K. Onnes, Leiden Comm. 120b 122b 124c (1911). Onnes received the Nobel prize in 1913 for the liquefication of Helium, not superconductivity - this can be found on the Nobel prize website (where Onnes Nobel lecture can also be obtained).--Dodecagon 21:55, 7 July 2007 (UTC)

---

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)

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 T_c [the critical temperature]. As the temperature is lowered to below T_c, 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)

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

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

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)

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)

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)

Did someone delete two image files associated with this article?

File:Superconducting-transition.png and File:Superconductor-b-vs-h.png are both missing. What's going on? —Preceding unsigned comment 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)

Deletion log File: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)

Deletion log File: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)

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.

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)

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)

the ambient temperature in space is very close to 3 degrees Kelvin. —Preceding unsigned comment added by 38.99.84.73 (talk) 23:33, 27 April 2008 (UTC)

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)

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.

-actually, since we'd get continuous savings from any improvement we make, the theoretical "savings" are infinite. It is true, however, that the low temperatures required for superconductivity are infeasible in the current infrastructure. —Preceding unsigned comment added by 38.99.84.73 (talk) 23:55, 27 April 2008 (UTC)

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.

“ And non-heating computers. The wires won't heat up, so small devices won't need cooling fans, and annoyingly large waste of space. ”

this is actually untrue. the computers themselves will make heat when they erase bits (ie, in every computation they perform) unless they are computers that utilize reversible computations) but the wires themselves won't heat up due to electrical resistance. —Preceding unsigned comment added by 38.99.84.73 (talk) 00:02, 28 April 2008 (UTC)

With any CMOS technology similar to today's, superconducting wires would make no difference to power dissipation. CMOS works by charging capacitors through resistors (devices and wires). The energy needed to do this is 1/2 CV^2 no matter where the R is located. So zero R wires would just lead to more dissipation in the devices, with the total unchanged. What superconducting wires *could* do is lead to faster operation. A good fraction of the delay in today's chips is due to the RC time constant of the wires themselves. A lower R (though it will not be zero, this is AC) would help here. So the chip might operate faster, but would take the same power when run at the same speed. LouScheffer (talk) 00:40, 28 April 2008 (UTC)

The anlysis by 38.99.84.73 was perceptive; new technologies are often oversold. But he missed some things. A large scale SC power system would require few transformers at all; the only reason we transform to (dangerously) high voltages is to transport power efficiently through resistive wires. SC cables could distribute power at the consumption voltage, say 5V. The whole infrastructure of overhead wires, giant pylons, switch stations, transformers, circuit breakers and wall warts could be junked. They would not need much electrical insulation at all, the current would preferentially flow through the superconductor. --Chetvorno^TALK 01:12, 26 September 2008 (UTC)

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)

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).

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, Gold-tin eutectic, Bismuth nanotubes, Graphine

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)

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)

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.

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)

"cannot" is correct. The article is trying to make the point that a superconductor acts differently than a hypothetical "perfect metal". (Maybe it's not making that point very well.) Spiel496 23:36, 17 April 2007 (UTC)

Breakthrough =

Might be interesting :

http://www.sciencedaily.com/releases/2007/05/070531135457.htm

--170.252.72.61 11:26, 1 June 2007 (UTC)

can someone elaborate on the breakthrough pls

Considered a definite answer to whether superconductors are metals or insulators...

http://www.publicaffairs.ubc.ca/media/releases/2007/mr-07-054.html?src=ubcca

I'd like to know more, too. Short answer: Good science, bad press release. Perhaps someone with access to the Nature article could help here. Here are my objections to the press release:

• It does not say what the material is. Other clues indicate it was YBCO or one of the other cuprate superconductors.
• It identifies the key discovery simply as "quantum oscillations" with no explanation -- as if the lay reader should know what that is. I think it refers to the De Haas-van Alphen effect which is exhibited by metals in a magnetic field.
• It implies that all experimental and theoretical progress has been stalled, waiting for the answer to a "yes" or "no" question.

For these reasons, I doubt the original premise that this experiment is "greatest advancement in superconductor research in a decade". Spiel496 03:40, 6 June 2007 (UTC)

According to the nature article, they measured the hall resistance ($R_{xy}$) of $YBa_{2}Cu_{3}O_{6.5}$ in a strong magnetic field (up to 62 T) applied normal to the copper oxide planes, with current applied along the a-axis. The hall resistance had an oscillatory component as a function of the inverse magnetic field: kind of like Shubnikov-De Haas effect. From this study they learned something about the Fermi surface it seems. Bamse 08:48, 6 June 2007 (UTC)

Flux Trapping & meissner effect

I want to start by saying that i am ot expert on superconductors. I consider myself a scientist with general knowledge on many subjects, thats it. I noticed in this page the meissner effect is mentioned several times, however its closely related flux trapping effect is not. In fact there is even an image posted of a magnet levitating above a superconductor indicating it is due to the meissner effect, when in fact it would be more accurate to describe it as the flux-trapping effect. My understanding is that the meissner effect does cause repulsion similar to diamagnetic material, when levitation occurs it is the flux trapping effect. When flux trapping occurs instead of straight up diamagnetism the magnet and the superconductor both attract and repel each other. Essentially the magnet will want to float at a particular distance, if you pull it away it will be pulled back to the superconductor, and if it is pushed closer it will be pushed away again. Until it reaches the point in the middle, thus giving you levitation. So i think this page needs a section on flux-trapping effect and correct a few of the parts that refer to the meissner effect to indicate flux-trapping instead. Debeo Morium 17:41, 7 August 2007 (UTC)

I remember seeing in a textbook a picture of a bar magnet levitating above a sheet of superconducting lead (Pb). Lead is a type-I superconductor, so there is no issue of flux-trapping. You don't need flux pinning to set a equilibrium distance. In the case of the magnet over lead, that distance is just where gravity and the magnet force happen to cancel each other. However, I also recall the lead sheet was bowl-shaped. I imagine this was to keep the magnet from simply sliding off to one side. My belief is that flux-pinning provides a restorative force in the horizontal direction. In other words, without flux-pinning, the magnet would still levitate via the Meissner effect, but it would immediately "slide" off to one side or the other. So, yes, in that picture one is seeing the actions of both flux-pinning and the Meissner effect, but the point is really the Meissner effect. When one sees the levitating magnet, the question that comes to mind is not "Why doesn't it slide off to the side?", but rather "Why does it levitate?". Spiel496 19:27, 7 August 2007 (UTC)

The flux-trapping effect does nto behave how you described at all. Just as an object can levitate above an object using flux-trapping, when you pick the magnet up the super conductor will dangle the same distance below the magnet off the ground. Such that the meissner efect and gravity are both pushing the superconductor down, it should fall to the ground if it wernt for the flux-trapping effect. Meissner effect appears to act as a repelling force, flux-trapping effect appears to repel or attract depending on distance, quiet different and as far as i know nothing at all like the meissner effect. Debeo Morium 21:20, 7 August 2007 (UTC)

I'm just describing a weaker example of the flux-trapping. Spiel496 06:32, 8 August 2007 (UTC)

After starting this thread and finding it a bit difficult to explain the difference between these two effects i wanted to show a video i just found that shows them fairly well: meissner effect vs. flux trapping Debeo Morium 01:03, 8 August 2007 (UTC)

Wow, that's an amazing video -- thanks for sharing the link. Regarding the flux-pinning vs Meissner effect distinction, we're really getting into semantics. The simplest behavior is that when a sample becomes superconducting, it expels the magnetic field, causing it to repel a magnet. If the magnet is above the superconductor, repulsion = levitation. In what are called Type II superconductors, the magnetic flux does penetrate the sample, confined to little non-superconducting lines called vortices. The situation gets a lot more complicated because the vortices may move around freely, or creep, or get pinned to defects (flux-trapping). Yes, all this affects how the magnet behaves, and in the case of that video the effects are really strong. But the Meissner effect is the more fundamental phenomenon, and that is responsible for the repulsion. The fact there are vortices at all is due in part to the Meissner effect. I advise strongly against muddying up that beautiful introductory image by introducing all of this into the caption. Spiel496 06:32, 8 August 2007 (UTC)

I think all this being said, it would be important to have a section somewhere on flux-trapping, and specify in the picture flux-trapping in place of meissner effect. The meissner effect may play a role in the flux-trapping effect. But the effect in that picture is of the flux trapping effect (with the meissner effect alone it would slide off the side no matter how you shape the super conductor underneath. Just like two magnets of opposing poles, you cant levitate it without a support keeping it from sliding off. Im not sure exactly why you oppose labeling the picture as the flux-trapping effect, seems to me from everything you said and everything I've looked up, thats exactly what it is. Of course i wont make the change until we atleast get a few more people giving their opinion, so id love to hear someone else chiming in too. Debeo Morium 02:25, 9 August 2007 (UTC)

I agree it is very important to distinguish the difference between the Meissner effect and flux-trapping. This is not simply a case of semantics, the difference maybe subtle but is highly important. Flux-trapping causes fixed levitation of magnets. Importantly flux-trapping tends to be a field-cooled effect i.e. as the type II superconductor is cooled in the presence of a magnetic field the field lines will become trapped in the superconductor in the form of vortices - Once in this state the superconductor will resist the removal of the vortices hence flux is trapped and the source of the flux is trapped - this effect is very different from the Meissner effect which arises from the generation of surface currents which generate a magnetic field which exactly opposes the applied field which leads to a repulsive `force' acting on any localised source of magnetic flux NOT a `holding' force as shown in the picture. --John 22:38, 9 August 2007 (UTC)

Another point occurred to me. Strictly speaking, a demonstration of the Meissner effect would be for a magnet resting on the superconductor to lift off as the material is cooled below T_c. That really happens, and that is the important point about the Meissner effect: magnetic flux is expelled as you cool below the transition temperature. From a still picture, one can't tell if that's how the hovering magnet got there. If it was brought to the SC after cooling, then it's really just a demonstration of zero electrical resistance. Flux-trapping also plays a role even in the true Meissner effect demonstration. The Meissner effect doesn't happen completely, so some flux lines remain stuck in the sample. If you try to move the magnet later, then there's a restoring force. Spiel496 03:12, 12 August 2007 (UTC)

Another area of the Meissner effect article that is very unclear is the constant referral to the penetration depth as the "London penetration depth". The London penetration depth is merely a penetration depth obtained from the solution of the London equations which fits the generalised definition of a penetration depth given in most graduate level textbooks - in reality this is different to the penetration depth quoted in the literature which is more general. Penetration depths also range from ~16nm for Al to ~200nm for YBCO.

Finally, the statement "The Meissner effect was explained by the brothers Fritz and Heinz London..." is incorrect - the London equations are phenomenological in nature i.e. they were derived by considering physical observations and a key assumption in deriving the London equations hence the London equations can be used to describe the behaviour of a superconductor but they do not explain the origins of the physical observations.--John 22:38, 9 August 2007 (UTC)

I could try to add the proper sections on flus-trapping and correct this. But i dont think im most qualified( but if the only one who will put in the time, i will). Anyone else want to add it who is up to the task who knows a thing or two about this topic? Debeo Morium 22:27, 10 August 2007 (UTC)

Well seeing as no one stepped up to add flux-trapping to the article im gonna start digging around and do my best to add the appropriate section and corrections. This is not a subject i am entirely educated on, so im sure my edits will need to be reviewed and changed. But i welcome any preliminary input before i take a crack at it. Debeo Morium 22:34, 20 August 2007 (UTC)

Meissner current

Please not that the superconductor underneath the levitating magnet is not in the Meissner phase. It is all about flux pinning in hard type-II superconductors. —Preceding unsigned comment added by 193.170.3.41 (talk) 12:31, 2 October 2007 (UTC)

a question

In the future can we hope for vehicles which work under the phenomenon of superconductivity? that is a vehicle made of magnet elevated on superconductor whose temperature is decreased below critical temperature? —Preceding unsigned comment added by Bhanuprakashapr (talk • contribs) 17:23, 26 October 2007 (UTC)

    -we already have transportation that operates under a similar principle, maglev trains.

Image:Meissner effect.jpg listed for deletion

An image or media file that you uploaded or altered, Image:Meissner effect.jpg, has been listed at Wikipedia:Images and media for deletion. Please see the discussion to see why this is (you may have to search for the title of the image to find its entry), if you are interested in it not being deleted. Thank you. Papa November (talk) 15:32, 28 January 2008 (UTC)

Please include the incomplete understanding of superconductivity

Someone more proficient with the subject should include in the article the problems current theories have as well as their incompleteness

e.g. http://www.physorg.com/news119272244.html

Slicky (talk) 18:54, 29 January 2008 (UTC)

The link you gave doesn't refer to any 'problems current theories have', just a new regime of superconductor action that doesn't obey the Ginsberg model. Superconductivity is an active field. Current theories explain the action of low temperature superconductors well, but new discoveries are made every week, and some areas, such as the mechanism that causes high temperature superconductivity, are still a mystery. This doesn't mean the existing theories are wrong. The article mentions that high temperature superconductivity is unexplained, although maybe it should be more prominently stated. --Chetvorno^TALK 00:20, 26 September 2008 (UTC)

Delisted from GA

In order to uphold the quality of Wikipedia:Good articles, all articles listed as Good articles are being reviewed against the GA criteria as part of the GA project quality task force. While all the hard work that has gone into this article is appreciated, unfortunately, as of February 18, 2008, this article fails to satisfy the criteria, as detailed below. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR.

As with many articles listed before the GA requirements were updated, this article is now lacking sufficient inline citations for GA status. I'll pass in on to the unreferenced GA task force; hopefully once citations have been added, the article will easily be able to reattain GA status. --jwanders^Talk 23:26, 18 February 2008 (UTC)

Perpetual motion machine

I am thinking about adding information on the idea that superconductors are related perpetual motion machines and I thought I could address some of the reasons for and against this idea. --Ilikemangos (talk) 07:11, 18 March 2008 (UTC)

room temp superconductivity

[1] --24.96.180.121 (talk) 02:28, 20 March 2008 (UTC)

That article is not one of EETimes' finest, to say the least. We need something better before adding content on this subject. There's no mention of the critical temperature, or anything quantitative for that matter. It's not even clear whether the resistivity of a sample was measured. According to [2] the researchers were able to compress silane to the point that the hydrogen density becomes high enough that a theory predicts superconductivity. Spiel496 (talk) 16:40, 20 March 2008 (UTC)

Why is Hebel-Slichter effect not mentioned?

I have recently written an piece (The Hebel-Slichter effect) on the field-cycling NMR experiment which led to the discovery of the Hebel-Slichter effect and on the role the latter played in confirming the BSC theory and continues to play in superconductivity research. I believe that the Hebel-Slichter effect is something that should definitely appear in any treatese on superconductivity, yet it is not included in the wiki article. I am afraid to include my page as an external link since I was just rebuked for including links to my own stuff. --Stan Sykora (talk) 15:46, 13 April 2008 (UTC)

Class of materials

It is stupid to redirect Superconductors to Superconductivity. Superconductors are a class of material. Superconductivity is a phenomenon. Is there any way to decouple this redirection? If not let's then have Semiconductors redirect to Semiconductivity. This is idiotic. —Preceding unsigned comment added by Freecat (talk • contribs) 02:36, 25 May 2008 (UTC)

I agree. Why not start an article about superconductors, as opposed to superconductivity. You can do this by editing the current re-direct page. LouScheffer (talk) 03:57, 25 May 2008 (UTC)

I notice also that "criminal" redirects to "crime"; "Protestant" redirects to "Protestantism"; "mammalian" redirects to "mammal". Often the class and the phenomenon are combined into one article when there's nothing else to say. What would this a "superconductor" article contain except to say "a material exhibiting superconductivity"? Spiel496 (talk) 13:43, 25 May 2008 (UTC)

This is a good point in general, but I suspect (I'm not an expert here) that's there is lots you could say about superconductors that does not go well into superconductivity. In particular, the practical aspects of making superconductors, and their practical uses, could go into 'superconductors', but does not fit well into 'superconductivity', which seems more of an explanation of the phenomenon and not practical matters. Just my two cents, LouScheffer (talk) 14:34, 25 May 2008 (UTC)

OK, I hadn't thought about that angle. Yeah, maybe there could be an article there. The article Technological applications of superconductivity exists, but it doesn't seem complete. Spiel496 (talk) 04:31, 26 May 2008 (UTC)

In my opinion it is better to treat those aspects as sections. It is much better having a good and complete article about a subject, than splitting it in 12 incomplete articles (unless, of course, the main article is already too big, but of course in that case we wouldn't have 12 incomplete articles, but probably 12 good articles). But Superconductivity is currently just 31k long, so it is much better if we expand it a bit before. Note that in other wikipedias the "many articles are better than one article" philosophy is quite different (see for example Frodo Beutlin/Frodo Baggins in the German wikipedia, which is redirected to the corresponding section of Middle Earth characters). Eynar Oxartum (talk) 12:20, 27 May 2008 (UTC)

I agree Superconductor should continue to redirect to this article. Superconductivity is the theory of how superconductive materials work, so 'superconductors' should be covered here. Maybe this article should include a list of superconducting materials, with their specifications (T_C, H_C, I_C, etc.) --Chetvorno^TALK 03:48, 11 October 2008 (UTC)

SnPbInBaTmCuO

I've removed the claim about 180K superconductivity in SnPbInBaTmCuO. I didn't do any kind of search to see if the claim is true, but the last time I looked into it, the only reference I could find was a patent showing a small change in resistivity near 180K. If the claim is really true, someone should be able to dig up a real reference. Spiel496 (talk) 17:30, 3 June 2008 (UTC)

procedure how superconducty is found

if u can help please which is needed for my studies —Preceding unsigned comment added by 122.167.69.1 (talk) 15:23, 4 June 2008 (UTC)

Classification by physical properties

The main article classifies superconductors by "their physical properties: they can be Type I (if their phase transition is of first order) or Type II (if their phase transition is of second order)." I think that this is incorrect. Can anybody fix this. TomyDuby (talk) 04:17, 12 July 2008 (UTC)

200 Kelvin superconductor?

http://www.superconductors.org/200K.htm

paramagnetic intrinsic Meissner effect

In the Meissner Effect section, this blurb [3] was recently added by 128.196.189.146. Is this notable? It's legitimate research, from a peer-reviewed paper. However, it's pretty obvious that 128.196.189.146 is the author of that paper. Spiel496 (talk) 04:19, 29 October 2008 (UTC)

I agree. Removed it. --Chetvorno^TALK 08:09, 29 October 2008 (UTC)