
[[Image:Meissner effect.jpg|thumb|300px|right|A magnet levitating above a "high-temperature" superconductor with boiling liquid nitrogen underneath demonstrates the Meissner effect.]] Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect.) In conventional superconductors, superconductivity is caused by a force of attraction between certain electrical conductions arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase (matter) composed of correlated ''pairs'' of electrons. There also exists a class of materials, known as unconventional superconductors, that exhibit superconductivity but whose physical properties contradict the theory of conventional superconductors. In particular, the so-called high-temperature superconductors superconduct at temperatures much higher than should be possible according to the conventional theory (though still far below room temperature.) There is currently no complete theory of high-temperature superconductivity. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys, some heavily-doped semiconductors, and certain ceramic compounds containing planes of copper and oxygen atoms. The latter class of compounds, known as the cuprates, are high-temperature superconductors. Superconductivity does not occur in coinage metal like gold and silver, nor in most ferromagnetism metals, though a number of materials displaying both superconductivity and ferromagnetism has been discovered in recent years. == Elementary properties of superconductors == Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have ''exactly'' zero resistivity to low applied currents when there is no magnetic field present. The existence of these "universal" properties imply that superconductivity is a phase (matter), and thus possess certain distinguishing properties which are largely independent of microscopic details. === Zero electrical resistance === Suppose we were to attempt to measure the electrical resistance of a piece of superconductor. The simplest method is to place the sample in an electrical circuit, in series with a voltage (potential difference) source ''V'' (such as a battery (electricity)), and measure the resulting current. If we carefully account for the resistance ''R'' of the remaining circuit elements (such as the leads connecting the sample to the rest of the circuit, and the source's internal resistance), we would find that the current is simply ''V/R''. According to Ohm's law, this means that the resistance of the superconducting sample is zero. Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in Magnetic resonance imaging machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years, and theoretical estimates for the lifetime of persistent current exceed the lifetime of the universe. In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat (which is essentially the vibrational kinetic energy of the lattice ions.) As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance. The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons, instead consisting of bound ''pairs'' of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the Hamiltonian of this Cooper pair fluid possesses an ''energy gap'', meaning there is a minimum amount of energy ''ΔE'' that must be supplied in order to excite the fluid. Therefore, if ''ΔE'' is larger than the thermal energy of the lattice (given by ''kT'', where ''k'' is Boltzmann's constant and ''T'' is the temperature), the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. In a class of superconductors known as type II superconductors (including all known high-temperature superconductors), an extremely small amount of resistivity appears when an electrical current is applied in conjunction with a strong magnetic field (which may be caused by the electrical current). This is due to the motion of vortex in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. === Superconducting phase transition === In superconducting materials, the characteristics of superconductivity appear when the temperature ''T'' is lowered below a critical temperature ''Tc''. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from less than 1K to around 20K. Solid Mercury (element), for example, has a critical temperature of 4.2K. As of 2001, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2), although this material displays enough exotic properties that there is doubt about classifying it as a "conventional" superconductor. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. (Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high ''T''''c''.) The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as ''e''−α/''T'' for some constant α. (This exponential behavior is one of the pieces of evidence for the existence of the energy gap.) The order of the superconducting phase transition is still a matter of debate. It had long been thought that the transition is second-order, meaning there is no latent heat. However, recent calculations have suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. === Meissner effect === When a superconductor is placed in a weak external magnetic field H, the field penetrates for only a short distance ''λ'', called the penetration depth, after which it decays rapidly to zero. This is called the Meissner effect. For most superconductors, the penetration depth is on the order of a hundred nm. The Meissner effect is sometimes confused with the "perfect diamagnetism" one would expect in a perfect electrical conductor: according to Lenz's law, when a ''changing'' magnetic field is applied to a conductor, it will induce an electrical current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from perfect diamagnetism because a superconductor expels ''all'' magnetic fields, not just those that are changing. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. A conductor in a static field, such as the dome of a Van de Graaff generator, will have a field within itself, even if there is no net charge in the interior. The Meissner effect was explained by London and London, who showed that the electromagnetic free energy in a superconductor is minimized provided : where H is the magnetic field and λ is the penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor exponential decay from whatever value it possesses at the surface. The Meissner effect breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value ''Hc''. Depending on the geometry of the sample, one may obtain an intermediate state consisting of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value ''H''''c''1 leads to a mixed state in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electrical current as long as the current is not too large. At a second critical field strength ''H''''c''2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called "fluxons" because the flux carried by these vortices is quantum. Most pure elemental superconductors (except niobium, technetium, vanadium and carbon nanotubes) are Type I, while almost all impure and compound superconductors are Type II. == Theories of superconductivity == Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Generalisations of these theories form the basis for understanding the closely related phenomenon of superfluidity, but the extent to which similar generalisations can be applied to unconventional superconductors as well is still controversial. == History of superconductivity == ''Main article : History of superconductivity'' Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistivity of solid mercury (element) at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistivity abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913. In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Walter Meissner and Robert Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Lev Davidovich Landau and Vitalij Lazarevics Ginzburg. This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger equation-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Alexei Alexeevich Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau having died in 1968.) Also in 1950, Maxwell and Reynolds ''et. al.'' found that the critical temperature of a superconductor depends on the isotope of the constituent chemical element. This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The complete microscopic theory of superconductivity was finally proposed in 1957 by John Bardeen, Leon Neil Cooper, and John Robert Schrieffer. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. The BCS theory was set on a firmer footing in 1958, when Bogoliubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian. In 1959, Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature. In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse Electric Corporation. In the same year, Brian David Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum ''h/e'', and thus (coupled with the quantum Hall effect) for Planck's constant ''h''. Josephson was awarded the Nobel Prize for this work in 1973. Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Johannes Georg Bednorz and Karl Alexander Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987). It was shortly found that replacing the lanthanum with yttrium, i.e. making YBCO, raised the critical temperature to 92 K, which was important because liquid nitrogen could then be used as a refrigerant (at atmospheric pressure, the boiling point of nitrogen is 77 K.) This is important commercially because liquid nitrogen can be produced cheaply on-site with no raw materials, and is not prone to some of the problems (solid air plugs, etc) of liquid helium in piping. Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics. == Technological applications of superconductivity == There have been many technological innovations based on superconductivity. Superconductors are used to make the most powerful electromagnets known to man, including those used in magnetic resonance imaging machines and the beam-steering magnets used in particle accelerators. They are also used to make SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. Superconductors have also been used to make digital circuits (e.g. based on the Rapid single flux quantum technology) and microwave filters for mobile phone base stations. Many promising applications of superconductivity have been stalled by the impracticality of maintaining large systems (e.g. long stretches of cable) at cryogenic temperatures. These problems may soon be alleviated with the continued development of high temperature superconductors, as these can be cooled by using liquid nitrogen rather than liquid helium (which is much more expensive and difficult to handle) or by using cryocoolers. However, the currently known high-temperature superconductors are brittle ceramics which are not easily turned into wires or other useful shapes. Promising future applications include high-performance transformers, SMES, electric power transmission, electric motors (e.g. for vehicle propulsion), and magnetic levitation devices. == Superconductors in science fiction == Superconductivity has long been a staple of science fiction. One of the first mentions of the phenomenon occurred in Robert Heinlein's novel ''Beyond This Horizon'' (1942). Notably, the use of a fictional room temperature superconductor was a major plot point in the ''Ringworld'' novels by Larry Niven, first published in 1970. Superconductivity is a popular device in science fiction due to the simplicity of the underlying concept - zero electrical resistance - and the rich technological possibilities. For example, superconducting magnets could be used to generate the powerful magnetic fields used by Bussard ramjets, a type of spacecraft commonly encountered in science fiction. The most troublesome property of real superconductors, the need for cryogenic cooling, is often circumvented by postulating the existence of room temperature superconductors. Many stories attribute additional properties to their fictional superconductors, ranging from infinite heat conductivity in Niven's novels (real superconductors conduct heat poorly, though superfluid helium has immense but finite heat conductivity) to teleportation in the Stargate film and TV series. In the movie Terminator 2 : Judgement Day, the CPU of the T800 destroyed in Terminator 1 is found to be superconductive at room temperature. == Links and references == === Selected references === ''Papers'' * H.K. Onnes, ''Commun. Phys. Lab.'' 12, 120 (1911) * W. Meissner and R. Oschenfeld, ''Naturwiss.'' 21, 787 (1933) * F. London and H. London, ''Proc. R. Soc. London'' A149, 71 (1935) * V.L. Ginzburg and L.D. Landau, ''Zh. Eksp. Teor. Fiz.'' 20, 1064 (1950) * E.Maxwell, ''Phys. Rev.'' 78, 477 (1950) * C.A. Reynolds et. al., ''Phys. Rev.'' 78, 487 (1950) * J. Bardeen, L.N. Cooper, and J.R. Schrieffer, ''Phys. Rev.'' 108, 1175 (1957) * N.N. Bogoliubov, ''Zh. Eksp. Teor. Fiz.'' 34, 58 (1958) * L.P. Gor'kov, ''Zh. Eksp. Teor. Fiz.'' 36, 1364 (1959) * B.D. Josephson, ''Phys. Lett.'' 1, 251 (1962) * J.G. Bednorz and K.A. Mueller, ''Z. Phys.'' B64, 189 (1986) === External links === *[http://www.eren.doe.gov/superconductivity/ US, EREN: superconductivity] *[http://www.superconductors.org/ superconductors.org] *[http://www.ornl.gov/reports/m/ornlm3063r1/pt1.html Introduction to superconductivity] === See also === * Timeline of low-temperature technology * Homes's law *Charge transfer complex vi:Siêu dẫn Condensed matter physics Electromagnetism Superconductivity
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
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-tate 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 ----- 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? User: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. --User: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? -- User: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''. ---- ==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. User:Pstudier 23:05, 2005 Jan 24 (UTC) The patent mentioned is: * Tesla, Nikola, [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=685012.WKU.&OS=PN/685012&RS=PN/685012 685,012], "''Means for Increasing the Intensity of Electrical Oscillations''". 1900 March 21. USPTO. User: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!--User: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. User: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? User: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. User: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. User: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.User: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. - User:Furrykef (User_talk:Furrykef) 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 [http://www.csicop.org/si/9201/minority.html this]. -- User: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). - User:Furrykef (User_talk:Furrykef) 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? User: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 ''super''conductor, when it is widely known to be a ''semi''conductor. 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. User: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. User:Deeceevoice 13:19, 7 Feb 2005 (UTC) :And, FYI, the earliest research (with which I'm familiar, at least) on the ''semi''conductivity 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. User:Deeceevoice 15:37, 7 Feb 2005 (UTC)
Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the expulsion of the interior magnetic field (the Meissner effect.) Electromagnetism Condensed matter physics
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[[Image:Meissner effect.jpg|thumb|300px|right|A magnet levitating above a "high-temperature" superconductor with boiling liquid nitrogen underneath demonstrates the Meissner effect.]] Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect.) In conventional superconductors, superconductivity is caused by a force of attraction between certain electrical conductions arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase (matter) composed of correlated ''pairs'' of electrons. There also exists a class of materials, known as unconventional superconductors, that exhibit superconductivity but whose physical properties contradict the theory of conventional superconductors. In particular, the so-called high-temperature superconductors superconduct at temperatures much higher than should be possible according to the conventional theory (though still far below room temperature.) There is currently no complete theory of high-temperature superconductivity. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys, some heavily-doped semiconductors, and certain ceramic compounds containing planes of copper and oxygen atoms. The latter class of compounds, known as the cuprates, are high-temperature superconductors. Superconductivity does not occur in coinage metal like gold and silver, nor in most ferromagnetism metals, though a number of materials displaying both superconductivity and ferromagnetism has been discovered in recent years. == Elementary properties of superconductors == Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature at which superconductivity is destroyed. On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have ''exactly'' zero resistivity to low applied currents when there is no magnetic field present. The existence of these "universal" properties imply that superconductivity is a phase (matter), and thus possess certain distinguishing properties which are largely independent of microscopic details. === Zero electrical resistance === Suppose we were to attempt to measure the electrical resistance of a piece of superconductor. The simplest method is to place the sample in an electrical circuit, in series with a voltage (potential difference) source ''V'' (such as a battery (electricity)), and measure the resulting current. If we carefully account for the resistance ''R'' of the remaining circuit elements (such as the leads connecting the sample to the rest of the circuit, and the source's internal resistance), we would find that the current is simply ''V/R''. According to Ohm's law, this means that the resistance of the superconducting sample is zero. Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in Magnetic resonance imaging machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years, and theoretical estimates for the lifetime of persistent current exceed the lifetime of the universe. In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat (which is essentially the vibrational kinetic energy of the lattice ions.) As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance. The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons, instead consisting of bound ''pairs'' of electrons known as Cooper pairs. This pairing is caused by an attractive force between electrons from the exchange of phonons. Due to quantum mechanics, the Hamiltonian of this Cooper pair fluid possesses an ''energy gap'', meaning there is a minimum amount of energy ''ΔE'' that must be supplied in order to excite the fluid. Therefore, if ''ΔE'' is larger than the thermal energy of the lattice (given by ''kT'', where ''k'' is Boltzmann's constant and ''T'' is the temperature), the fluid will not be scattered by the lattice. The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. In a class of superconductors known as type II superconductors (including all known high-temperature superconductors), an extremely small amount of resistivity appears when an electrical current is applied in conjunction with a strong magnetic field (which may be caused by the electrical current). This is due to the motion of vortex in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. === Superconducting phase transition === In superconducting materials, the characteristics of superconductivity appear when the temperature ''T'' is lowered below a critical temperature ''Tc''. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from less than 1K to around 20K. Solid Mercury (element), for example, has a critical temperature of 4.2K. As of 2001, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2), although this material displays enough exotic properties that there is doubt about classifying it as a "conventional" superconductor. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The explanation for these high critical temperatures remains unknown. (Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high ''T''''c''.) The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as ''e''−α/''T'' for some constant α. (This exponential behavior is one of the pieces of evidence for the existence of the energy gap.) The order of the superconducting phase transition is still a matter of debate. It had long been thought that the transition is second-order, meaning there is no latent heat. However, recent calculations have suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. === Meissner effect === When a superconductor is placed in a weak external magnetic field H, the field penetrates for only a short distance ''λ'', called the penetration depth, after which it decays rapidly to zero. This is called the Meissner effect. For most superconductors, the penetration depth is on the order of a hundred nm. The Meissner effect is sometimes confused with the "perfect diamagnetism" one would expect in a perfect electrical conductor: according to Lenz's law, when a ''changing'' magnetic field is applied to a conductor, it will induce an electrical current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from perfect diamagnetism because a superconductor expels ''all'' magnetic fields, not just those that are changing. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law. A conductor in a static field, such as the dome of a Van de Graaff generator, will have a field within itself, even if there is no net charge in the interior. The Meissner effect was explained by London and London, who showed that the electromagnetic free energy in a superconductor is minimized provided : where H is the magnetic field and λ is the penetration depth. This equation, which is known as the London equation, predicts that the magnetic field in a superconductor exponential decay from whatever value it possesses at the surface. The Meissner effect breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value ''Hc''. Depending on the geometry of the sample, one may obtain an intermediate state consisting of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value ''H''''c''1 leads to a mixed state in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electrical current as long as the current is not too large. At a second critical field strength ''H''''c''2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called "fluxons" because the flux carried by these vortices is quantum. Most pure elemental superconductors (except niobium, technetium, vanadium and carbon nanotubes) are Type I, while almost all impure and compound superconductors are Type II. == Theories of superconductivity == Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Generalisations of these theories form the basis for understanding the closely related phenomenon of superfluidity, but the extent to which similar generalisations can be applied to unconventional superconductors as well is still controversial. == History of superconductivity == ''Main article : History of superconductivity'' Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistivity of solid mercury (element) at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistivity abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913. In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Walter Meissner and Robert Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Lev Davidovich Landau and Vitalij Lazarevics Ginzburg. This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger equation-like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Alexei Alexeevich Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau having died in 1968.) Also in 1950, Maxwell and Reynolds ''et. al.'' found that the critical temperature of a superconductor depends on the isotope of the constituent chemical element. This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The complete microscopic theory of superconductivity was finally proposed in 1957 by John Bardeen, Leon Neil Cooper, and John Robert Schrieffer. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. The BCS theory was set on a firmer footing in 1958, when Bogoliubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian. In 1959, Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature. In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse Electric Corporation. In the same year, Brian David Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. It is used in the most accurate available measurements of the magnetic flux quantum ''h/e'', and thus (coupled with the quantum Hall effect) for Planck's constant ''h''. Josephson was awarded the Nobel Prize for this work in 1973. Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. In that year, Johannes Georg Bednorz and Karl Alexander Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987). It was shortly found that replacing the lanthanum with yttrium, i.e. making YBCO, raised the critical temperature to 92 K, which was important because liquid nitrogen could then be used as a refrigerant (at atmospheric pressure, the boiling point of nitrogen is 77 K.) This is important commercially because liquid nitrogen can be produced cheaply on-site with no raw materials, and is not prone to some of the problems (solid air plugs, etc) of liquid helium in piping. Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics. == Technological applications of superconductivity == There have been many technological innovations based on superconductivity. Superconductors are used to make the most powerful electromagnets known to man, including those used in magnetic resonance imaging machines and the beam-steering magnets used in particle accelerators. They are also used to make SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. Superconductors have also been used to make digital circuits (e.g. based on the Rapid single flux quantum technology) and microwave filters for mobile phone base stations. Many promising applications of superconductivity have been stalled by the impracticality of maintaining large systems (e.g. long stretches of cable) at cryogenic temperatures. These problems may soon be alleviated with the continued development of high temperature superconductors, as these can be cooled by using liquid nitrogen rather than liquid helium (which is much more expensive and difficult to handle) or by using cryocoolers. However, the currently known high-temperature superconductors are brittle ceramics which are not easily turned into wires or other useful shapes. Promising future applications include high-performance transformers, SMES, electric power transmission, electric motors (e.g. for vehicle propulsion), and magnetic levitation devices. == Superconductors in science fiction == Superconductivity has long been a staple of science fiction. One of the first mentions of the phenomenon occurred in Robert Heinlein's novel ''Beyond This Horizon'' (1942). Notably, the use of a fictional room temperature superconductor was a major plot point in the ''Ringworld'' novels by Larry Niven, first published in 1970. Superconductivity is a popular device in science fiction due to the simplicity of the underlying concept - zero electrical resistance - and the rich technological possibilities. For example, superconducting magnets could be used to generate the powerful magnetic fields used by Bussard ramjets, a type of spacecraft commonly encountered in science fiction. The most troublesome property of real superconductors, the need for cryogenic cooling, is often circumvented by postulating the existence of room temperature superconductors. Many stories attribute additional properties to their fictional superconductors, ranging from infinite heat conductivity in Niven's novels (real superconductors conduct heat poorly, though superfluid helium has immense but finite heat conductivity) to teleportation in the Stargate film and TV series. In the movie Terminator 2 : Judgement Day, the CPU of the T800 destroyed in Terminator 1 is found to be superconductive at room temperature. == Links and references == === Selected references === ''Papers'' * H.K. Onnes, ''Commun. Phys. Lab.'' 12, 120 (1911) * W. Meissner and R. Oschenfeld, ''Naturwiss.'' 21, 787 (1933) * F. London and H. London, ''Proc. R. Soc. London'' A149, 71 (1935) * V.L. Ginzburg and L.D. Landau, ''Zh. Eksp. Teor. Fiz.'' 20, 1064 (1950) * E.Maxwell, ''Phys. Rev.'' 78, 477 (1950) * C.A. Reynolds et. al., ''Phys. Rev.'' 78, 487 (1950) * J. Bardeen, L.N. Cooper, and J.R. Schrieffer, ''Phys. Rev.'' 108, 1175 (1957) * N.N. Bogoliubov, ''Zh. Eksp. Teor. Fiz.'' 34, 58 (1958) * L.P. Gor'kov, ''Zh. Eksp. Teor. Fiz.'' 36, 1364 (1959) * B.D. Josephson, ''Phys. Lett.'' 1, 251 (1962) * J.G. Bednorz and K.A. Mueller, ''Z. Phys.'' B64, 189 (1986) === External links === *[http://www.eren.doe.gov/superconductivity/ US, EREN: superconductivity] *[http://www.superconductors.org/ superconductors.org] *[http://www.ornl.gov/reports/m/ornlm3063r1/pt1.html Introduction to superconductivity] === See also === * Timeline of low-temperature technology * Homes's law *Charge transfer complex vi:Siêu dẫn Condensed matter physics Electromagnetism Superconductivity
Superconductivity
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
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-tate 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 ----- 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? User: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. --User: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? -- User: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''. ---- ==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. User:Pstudier 23:05, 2005 Jan 24 (UTC) The patent mentioned is: * Tesla, Nikola, [http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=685012.WKU.&OS=PN/685012&RS=PN/685012 685,012], "''Means for Increasing the Intensity of Electrical Oscillations''". 1900 March 21. USPTO. User: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!--User: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. User: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? User: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. User: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. User: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.User: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. - User:Furrykef (User_talk:Furrykef) 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 [http://www.csicop.org/si/9201/minority.html this]. -- User: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). - User:Furrykef (User_talk:Furrykef) 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? User: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 ''super''conductor, when it is widely known to be a ''semi''conductor. 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. User: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. User:Deeceevoice 13:19, 7 Feb 2005 (UTC) :And, FYI, the earliest research (with which I'm familiar, at least) on the ''semi''conductivity 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. User:Deeceevoice 15:37, 7 Feb 2005 (UTC)
Superconductivity
Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the expulsion of the interior magnetic field (the Meissner effect.) Electromagnetism Condensed matter physics
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