|WikiProject Physics||(Rated Start-class, Mid-importance)|
- 1 wrong picture
- 2 light
- 3 Article Needs A Section on Potential Applications
- 4 Article too brief
- 5 Page inaccurate
- 6 Factual inaccuracy in theory
- 7 History?
- 8 Simplified a little?
- 9 absorption, or reflection?
- 10 Apparent contradiction
- 11 type-II type-I
- 12 Biological?
- 13 Distinct from perfect conductors?
- 14 Deleted Observation Section
- 15 What about the equals case
- 16 The article is not complete
- 17 Nobody Knows
- 18 Merge superdiamagnetism here
- 19 Flux pinning
- 20 Upside down, boy you turn it, inside out, and round and round
- 21 A distinction must be made
- 22 Hirsch
as I was doing the same mistake in a presentation that a gave about superconductivity, I want to note that the picture with the hovering magnet above a superconductor os not the observation of the Meißner-Ochsenfeld effect. The observation of a flying magnet is due to the creation of vortices in a type II superconductor.. see shubnikov state.. The Meißner effect cannot explain the force that elliminate the gravitation.. since the picture suggests that this effect is the reson for it I would replace it.. cheers --Xeltok (talk) 18:07, 20 January 2009 (UTC)
you think maybe you could do kinda the same thing with light. Bend it around somthing that is not affected by it?
gravity bends light...that's how we know of the existence of black holes. we see where a star's supposed to be, and where we see it as being, and so we know that there's a superdense celestial body somewhere in between. so yeah. the effect is similar with light.
Article Needs A Section on Potential Applications
Article needs a section on what the potential practical applications may be for the Meissner Effect.
Article too brief
Much is left to be said about the Meissner effect, including experimental methods for measurement and historical discussion. Overall, the page is lacking in content.
As in too many of the physics explanations on Wikipedia, the explanation of how the Meissner effect works assumes the reader is nearly a physics expert and is inadequate at best for general science readers with reasonable backgrounds in the physical sciences. —Preceding unsigned comment added by 220.127.116.11 (talk) 00:19, 18 June 2008 (UTC)
"This active exclusion of magnetic fields is distinct from perfect diamagnetism." This sentence is confusing. From the book High-Temperature Superconductivity by Genrald Burns, it is said that:""Thus in a weak magnetic field, a superconductor has perfect diamagnetism, a phenomenon called the Meissner effect." So Meissner effect is a diamagnetic phenomenon?
chianshin 09:40, 10 April 2007 (UTC)
There is no such thing as the Laplacian of B. That's just incorrect. B is a vector quantity. I don't enough about the actual theory to correct the page, but this page needs to be fixed up.
Mgummess 16:04, 31 March 2007 (UTC)
- Yes, there *is* such a thing as the Laplacian of a vector quantity. Since is a scalar operator, it operates on each component of the vector, i.e.
Superconductivity#Meissner_effect is more comprehensive for the most part and integrates the topic into its natural category. This article does contain some information and images not present in the Superconductivity article and should be merged.KF6AUF
- Do not merge; stand-alone topics are conducive to learning; (online) article length is inversely proportional to information-acquisition.--Sadi Carnot 17:36, 19 February 2006 (UTC)
- Better merge the information from Superconductivity to Meissner effect. vedant (talk • contribs) 13:15, 24 February 2006 (UTC)
- It would be good to have a brief, phenomenological description of the M. effect on the superconductivity page and then a link to a longer article here. Why limit the amount of information on wikipedia or have excessively long articles?
I came to this article looking for a non-technical answer as to why the Meissner effect happens. I left the article still thirsting for knowledge. How about a brief non- (less?) technical description of what's going on? -Mr.Logic 17:40, 22 March 2006 (UTC)
As of 15:40PST on 17 May 2006, this article and the article on perfect diamagnetism are very similar, with the notable difference that this article says "Note that there is a difference between a perfect diamagnet and a superconductor," while the article on perfect diamagnetism says the exact opposite.
Factual inaccuracy in theory
The meissner effect is distinct from perfect diamagnetism arising from zero resistance. The theory described in the article, as it stands now is wrong. There's no reference to the london equations. I lack the time, so can someone fix it? I'll try editing myself if I have the time siddharth 08:28, 8 June 2006 (UTC)
- There, I've showed that the meissner effect is distinct from perfect diamagnetism. siddharth 18:07, 14 June 2006 (UTC)
Reworded this to make it clearer, shorter sentances and rearranged. Just to exaggerate the distinction between perfect diamagnetism and screening currents (meissner effect) which are different phenomena however exhibt the same behavour outside the superconductor.
"Diamagnetism: Diamagnetic properties arise from the realignment of the electron orbits under the influence of an external magnetic field." This is NOT screening currents. User:joshsiret 09:49 12 August 2010 (GMT) —Preceding unsigned comment added by 18.104.22.168 (talk)
How was this discovered? — Omegatron 01:49, 19 June 2007 (UTC)
Simplified a little?
I was reading this article like someone who doesn't know a thing about it, and well, yes, I had some trouble trying to understand it. Can anyone just explain to me how the liquid nitrogen affects the magnet and makes it a superconductor?
the answer is that a material doesn't attain superconductivity until it's below a certain temperature. The temperature varies for each material. some superconducting materials are lead, mercury and aluminum.
absorption, or reflection?
from the illustration given, it's unclear whether the Meissner effect can be used to focus a magnetic field (as with a parabolic solar oven focusing light) or if the material used simply stops the magnetic field from going beyond the material's penetration depth. 22.214.171.124 (talk) 17:37, 4 April 2008 (UTC)AI#0
- Like a rock in a stream, the field is simply expelled from the material, and go around it, generally. 126.96.36.199 (talk) 01:14, 13 June 2012 (UTC)
The article says that "Observation of the Meissner effect is difficult, because the applied fields have to be relatively small (the measurements need to be made far from the phase boundary)." It also shows a refrigerator magnet levitating over a superconductor. I assume that what the original author meant is that measurements of the Meissner effect are difficult because using a particular method of calculation requires a small applied field, but I'm no expert. Wnt (talk) 21:46, 21 May 2008 (UTC)
Is the Meissner effect a property of all superconductors or just Type-I superconductors? I ask because Talk:Yttrium barium copper oxide suggests it does not apply to Type-II superconductors. Rod57 (talk) 00:59, 5 September 2008 (UTC)
- I believe the Meissner effect is a property of all superconductors, and can be derived by the application of Faraday's law of induction to the surface of the superconductor. As the flux attempts to cut the surface it induces surface currents that cancel out the original field (by Lenz's law). As far as I can see the type II discussion is talking about penetration beyond a certain field strength. I believe (although am less sure) that this is also common to all superconductors. --Michael C. Price talk 13:26, 30 June 2009 (UTC)
- Following some of the external links I see that In Type II superconductors the magnetic field is not excluded completely, but is constrained in filaments within the material. So depending on how you define the Meissner effect you could argue it either way, since the interior of the filaments are not superconducting themselves. --Michael C. Price talk 19:26, 30 June 2009 (UTC)
Some friends I know from the nearby University have started studying the Meissner affect. We know it affects magnet, but everything generates magnetism from their mass, so we were wondering if Biological objects like plants or even people can be suspended using this effect?188.8.131.52 (talk) 16:25, 10 November 2008 (UTC)
- In some sense a superconductor is a perfect diamagnet. Living things tend to be weakly diamagnetic, i.e. they naturally repel magnetic fields to a tiny degree. Good diamagnets such as pyrolytic carbon will happily levitate over a suitable geometry of regular shop-bought Neodymium-Iron-Boron supermagnets. Living things can be magnetically levitated but typically require unusually strong fields. I've seen a video of a frog being levitated inside what I think was an NMR cavity and the same was recently performed with a mouse, attracting some media attention. This could entail anything between 1 and 20 tesla fields. I'm willing to guess that people have studied protists and such in similar conditions. Suffice to say that you can suspend biological objects but it requires tremendously strong fields even for small objects. For comparison, the strongest permanent magnet created thus far has a strength of ~5 tesla. NMRs use Superconducting magnets. Eutactic (talk) 04:53, 2 December 2009 (UTC)
Distinct from perfect conductors?
The article states:
- The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconducting state.
But I thought that conductors also excluded E & B fields via induced surface currents and charges. Not as well as superconductors, of course, but nevertheless this is merely a difference of degree, not one of kind. --Michael C. Price talk 21:19, 27 June 2009 (UTC)
- This is partly true and partly false--- if a perfect conductor starts out with no magnetic field inside, it will not allow any new magnetic fields to enter. But there is no obvious reason in theory that a pre-existing magnetic field will be expelled. If a conductor is perfect and a magnetic field is already inside, the field will just be frozen at the value it had when the material became a perfect conductor.
- The Meissner effect showed that the magnetic field in a superconductor is expelled. Not only that, but it showed that the field needed to get expelled in order to get to the superconducting state, since the transition temperature in a magnetic field is lower than the transition temperature at zero field. That means that the field is thermodynamically "pushing" the material to stay in the normal state, it acts as a thermodynamic potential to stabilize the normal metal.Likebox (talk) 16:42, 30 June 2009 (UTC)
- I don't know enough condensed / solid-state physics to see the mechanism, but it is a neat analogy. Presumably cosmic strings are the analogues of the magnetic field intrusion in type II s-conductors? --Michael C. Price talk 10:00, 1 July 2009 (UTC)
Interesting reference on the topic: http://ajp.aapt.org/resource/1/ajpias/v80/i2/p164_s1 — Preceding unsigned comment added by 184.108.40.206 (talk) 12:19, 3 July 2012 (UTC)
Deleted Observation Section
The section titled "Observation" is incorrect. First of all, measurement of the Meissner effect, to a satisfactory number of significant figures, predate the 1985 discovery of high-temperature superconductor by a generation or more. For example one might wind a coil of insulated copper wire around the sample (carefully noting the number N of turns). Now place this - in a Dewar containing liquid helium - between the poles of an electromagnet. Next turn the electromagnet on while the sample is still a normal conductor and measure the time integral of the induced voltage - using an Integrating Voltmeter. This voltage impulse - in volt-seconds - equals N times the flux admitted - in webers. Now cool the sample through the superconducting transition and obtain the FLUX EXPELLED (Meissner effect), Then compare the two!
The section titled "Observation" also erroneously implies the levitation of a permanent magnet by a superconductor was possible only with high-temperature superconductors. Not so!
Finally, statements implying that still-photographs of "Levitation of a Permanent Magnet" prove the Meissner effects are erroneous. If you bring the magnet to the superconductor from a distance and it ends up levitating, you have only proved the PERFECT CONDUCTIVITY of the superconductor! On the other hand, if you FIRST place the magnet on the surface of the sample in its normal state and THEN cool it down into a superconductor, THEN, IF IT JUMPS UP AND LEVITATES, or shows that it is trying to do that, with, say, one pole up and the other trapped, THAT WOULD PROVE THE EXPULSION OF FLUX (Meissne effect.) -- Alfred Leitner
- I have undone the deletetion. Before this edit by me it said that the Meissner effect was difficult to observe. And that is true - it took many years after the discovery of superconductivity untill Meissner. And even then it was difficult, usually detected by changes in the magnetic field. The amazing thing with high-Tc was that one could do this in air, on the table. And yes, cooling willmake the magnet go up of course - easily demonstrated with high-Tc's. /Pieter Kuiper (talk) 00:16, 22 September 2009 (UTC)
- I agree with the deletion. The Meissner effect was discovered long before high Tc (1933). Measuring small changes in magnetic field is not particularly difficult, especially since the advent of the SQUID in the 1960s.Tls60 (talk) 18:55, 13 May 2012 (UTC)
What about the equals case
The article is not complete
Unless someone edits in quantum levitation 
That is based on Meissner effect (in fact, some magnetic flux tubes still penetrate an extremely thin coating of superconductor, that is what enables such demonstration). — Preceding unsigned comment added by 220.127.116.11 (talk) 14:51, 18 October 2011 (UTC)
- "Quantum levitation" is established terminology based upon the casimir force: http://www.st-andrews.ac.uk/~ulf/levitation.html 18.104.22.168 (talk) 18:07, 19 October 2011 (UTC)
Doing my proffesional skills III module at the university of york I had great trouble trying to understand what actually causes the the meissner effect. In short nobody knows! I've added that "no dynamical explanation of the Meissner effect exists within the conventional understanding of superconductivity"
Doing my professional skills III module at the university of york I had great trouble trying to understand what actually causes the meissner effect. In short nobody knows! I've added that "no dynamical explanation of the Meissner effect exists within the conventional understanding of superconductivity" — Preceding unsigned comment added by Chronus15 (talk • contribs) 02:38, 9 December 2011 (UTC)
Actually, yes they do.
The Meissner effect arises out of BCS theory, the ultimate microscopic theory of SC, from which the penetration depth can be derived for a superconductor both with a current density J and under applied magnetic field H. Therefore the 'cause' of the Meissner effect is the same as the 'cause' of superconductivity - the formation of a Cooper pair condensate, which in turn results in the normal screening currents at the edge, the expulsion of field and all the other aspects that the Londons described phenomenologically.
The objections of Jorge Hirsch relate to the *precise dynamics* of this process i.e. - the exact dynamics of how the pair condensate and normal state regions form. NOT the actual physical origin of them, of superconductivity or reasons for field exclusion, both of which arise (via quite some calculation admittedly) from the theory of BCS.
The actual physical origin of the Meissner effect is quite hard to understand, having to do with gauge symmetry (http://prola.aps.org/abstract/PR/v111/i3/p817_1) all from the BCS theory. A simplified picture is given here http://www.nature.com/nature/journal/v433/n7023/full/nature03281.html. The best analogy is that a single electron is a brick - you don't need much energy to move it. The assembly of superconducting electrons - the Cooper pairs - is a wall, interlocking together to form a stronger structure. This 'wall' requires far more energy to knock it down or penetrate it than the single brick. In the case of the superconducting pair state, this 'energy' is a photon - or in other words, a magnetic field - which now has an energy 'cost' to get throught he state and hence can no longer penetrate. Or by analogy, the photon is a 'bullet' which is now deflected by the 'wall' in a manner a single brick or pile of random bricks never could.
This is difficult stuff, doubt they cover it in a general professional skills class!
Merge superdiamagnetism here
- Agree - since there are no objections I'm going ahead with the merger, with superdiamagnetism becoming a redirect to Meissner effect. Tls60 (talk) 19:52, 13 May 2012 (UTC)
The article currently does not explain why the magnet stays in place in the leveitation examples, rather than sliding over the expelled field, this is explained at Flux pinning - perhaps a few sentences here would be helpful? 22.214.171.124 (talk) 15:52, 8 April 2013 (UTC)
Upside down, boy you turn it, inside out, and round and round
As many astronomical bodies do have a Magnetic Field, and there may be Magnetic Fields more or less intense all across the universe, if a Magnet, i.e., something having a Magnetic Field, levitates over a Superconductor, the phenomenon could be reversed, the way the shape of a Wankel engine housing was changed by an inversion, from the early designs where both housing and piston rotated, to the currently used ones, with a rotating piston and a fixed stator, epitrochoid or housing; thus, is it possible that a superconducting body or a superconducting part inside a bigger device may levitate on the existing natural magnetic fields, if the adequate power or any other differential physical dymension is implemented or applied? Salut † --Jgrosay (talk) 14:26, 23 October 2013 (UTC)
A distinction must be made
From my brief reading here, it seems to me that a very fine distinction exists between perfect diamagnetism of a perfect conductor and the Meissner effect of a superconductor. I intend to address the inconsistencies I see here.
A superconducting pellet (good ol' Y123) is brought below its transition temperature with LN2 in a styrofoam cup. A small rare-earth magnet (NdFeB) is placed above the pellet, and is observed to levitate at a fixed spacing. Attempts to push the magnet closer to the SC pellet show that the magnet prefers to return to it's original spacing above the pellet. This is the Meissner effect, as I have been informed by faculty.
My professor's attempt to articulate the theory led me to believe that surface-depth eddy currents induced in opposition to the applied B field are the cause of the so-called Meissner effect. He disclaimed expertise over the minutae of BCS theory and left it there in class. However, from what I read here, what my professor described is in fact perfect diamagnetism and not the "exclusion of internal B" via the Meissner effect.
My difficulty in understanding arises here: has there ever been a material observed to display perfect diamagnetism that does not display the Meissner effect? Moreover, is there any material which is a perfect conductor but not a superconductor? It seems to me like perfect diamagnetism is an older explanation for what is observed to be B field internal exclusion when observations are performed on a sample already below Tc. The two effects would not be distinguishable unless the transition temperature was traversed while a constant applied B
So my question stands: has perfect diamagnetism ever been observed without the presence of the Meissner effect? It seems to me like perfect diamagnetism is merely an overly simple explanation which appeals to the formulae of Lenz and Faraday. If indeed there has been such an observed "internal freezing of an external B field", I would most love to be aware of it. Otherwise, the distinction seems redundant. — Preceding unsigned comment added by 126.96.36.199 (talk) 16:54, 6 March 2014 (UTC)
I think one should not mention J. Hirsch's complaints about BCS theory. These are extremely fringe theory -- I think a poll among practicing physicists would find 99.999% disagree with such fringe theories. However, scientific truth is not decided by polls. In 1542, 99.99% of practicing astronomers agreed with Ptolemy's model of the solar system.