[different materials, currently most operational ones require very expensive-to-maintain cold liquids; however, there are some that are starting to be room-temperature (though under extreme pressure, like the silanes family of hydrogen--SH4, like methane though with a sulfur instead of a carbon--and then heavily pressured and it yields superconduction; the Nick Cook book has a section on superconduction as well in exotic materials]
Room Temperature Superconductors
7 min
"This overview of the polymer-based superconductive "ultraconductors" describes an ongoing research project by Room Temperature Superconductors, Inc, located in Sebastopol, CA. They already have a working prototype, and are seeking capital investment to complete the project, which will deliver a lightweight polymer cabling with a conductivity 100,000 greater than copper wire. The future is here! Ultraconductors will enable a new generation of high-power, high-efficiency electrical transmission & power equipment, and will impact ever aspect of human life from consumer electronics & faster microprocessors to reduced environmental pollution & electrical losses in long-distance transmission lines. Check out their site at www.ultraconductors.com."
Another version of Room-temperature superconductors is a step closer with silane--though it requires high pressures to make the 'high pressure hydrogen metal'.
By Chris Lee | Published: March 19, 2008 - 07:41PM CT
Superconductivity was first observed when Onnes used liquid helium to cool mercury.
It was soon found that quite a few metals would superconduct when cooled to within a few degrees of absolute zero. However, the dream of superconductivity at higher temperatures—perhaps even room temperature—has kept researchers pursuing superconductivity.
Now, new research on a class of chemicals has yielded some interesting results that may point superconductor research in a different direction: hydrogen-based compounds.
Related Stories
* Superconductor breakthroughs abound: some like it hot
* High temperature superconductors, 20 years on
Despite the attraction of low-loss superconductors, the cooling demands have limited the application of superconductivity to very high field magnets, such as those used in magnetic resonance imaging devices.
In the 1980s, a new form of superconductivity that operated at liquid nitrogen temperatures got everyone pretty excited. Unfortunately, these ceramics are hard to make, harder to handle, and don't carry much current, making them even less useful than their lower-temperature brethren.
What we need is a substance that has the more robust superconductivity and handling properties of metallic superconductors while retaining the high transition temperature of the ceramics. In short, a different kind of metal.
The ultimate choice would be hydrogen, which, under sufficient pressure, is thought to become metallic. Calculations suggest that the structure and properties of metallic hydrogen would support superconductivity at quite a high temperature.
On the other hand, this is just so much mental masturbation, because hydrogen isn't expected to become metallic until pressures of 400GPa—a bit of a squeeze for current lab equipment. Nevertheless, there are several hydrogen-like alternatives, where a compound with lots of hydrogen in it is put under sufficient pressure to become a metal. This works because the presence of the heavier atomic cores act to compress the electrons surrounding the hydrogen nucleus, meaning that it is, in effect, already under a significant amount of pressure. This brings down the metallic transition pressure, putting it within the reach of lab equipment.
This is exactly why researchers at Max Planck Institute for Chemistry have been putting the squeeze on silane. Silane is a silicon atom surrounded by four hydrogen atoms, making it one of two perfect candidates for hydrogen-based metals (the other is methane). They found that silane became metallic at around 50GPa, which is still a pretty substantial pressure. On cooling, the metallic silane begins to superconduct.
However, the temperature at which superconductivity occurs exhibits some interesting behavior. It hangs around 5-10K for most of the pressure range (50-200GPa), but in a small range between 100-125GPa, it increases quite sharply. Although the researchers only have five data points in the range and never observed a critical temperature higher than 20K, the shape of the curve indicates that, for some small range of pressures, a very high critical temperature might be achieved.
A note of caution should be injected at this point: DO NOT TRY THIS AT HOME. Silane is a gas at room temperature and pressure. It is a gas that you will not find naturally occurring because it spontaneously combusts in air. In fact, one can imagine that wires and magnets based on a silane superconductor would also make wonderful pipe bombs—not something that you want in the same room as a million-dollar MRI machine. On a slightly more serious note, the higher the required critical temperature, the narrower the pressure range for which superconductivity can be achieved, meaning that very high quality pressure control would be required to maintain silane in a useful state. All in all, it is hard to tell if this a win for superconductivity. It is, however, certainly a win for materials research.
Science, 2008, DOI: 10.1126/science.1153282
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http://arstechnica.com/news.ars/post/20080319-room-temperature-superconductors-a-step-closer-with-silane.html
2.
World's first hybrid superconducting electrical cable tests successful
26.03.2012
World's first hybrid superconducting electrical cable tests successful.
Russian scientists have successfully tested the world's first hybrid superconducting electrical cable. This small cable consists of magnesium diboride, a superconductor, and a cavity for the transportation of liquid hydrogen. The latter, while cooling diboride to a temperature of 40 degrees Kelvin, causes the effect of superconductivity.
The problem of superconductivity, that is, the material's ability to conduct electricity without resistance, has been the subject of much attention from scientists and engineers since the beginning of the last century.
Indeed, if it were possible to manufacture this material on an industrial scale, the threat of an energy crisis could be forgotten.
In addition, the introduction of superconductors would encourage the development of alternative energy, for example, solar energy.
An interesting project on the subject was presented at a symposium at the Institute for the study of environmental sustainability in Potsdam, Germany in May of last year by the famous physicist Alex Muller. According to his calculations, if we were to install solar panels on the area of 300 square kilometers in the Sahara desert with 360 sunny days a year, they would produce as much electricity as is now produced by all power stations in the world. To cover the electricity needs of the entire Europe, a battery with an area of 50 square kilometers would be sufficient.
Needless to say, it sounds tempting if it was not for one caveat. In order for this project to be implemented, superconductors are required. Otherwise, the electricity from the Sahara would not reach even the south of Europe as it would be spent on overcoming the resistance of the material. At the same symposium, as a result of discussions among scientists, it was found that only lines of constant current are suitable for the transmission of electricity over long distances (e.g., three to five thousand kilometers). The popular air transmission lines AC have limitations in terms of length and can only stretch for several hundred kilometers. The power should be approximately ten gigawatts.
In principle, if cable was made of superconducting material, there would be no problems. But here is the issue - all superconductors known to scientists flatly refuse to show their wonderful properties at normal for us temperatures. The effect of superconductivity occurs most often at temperatures close to absolute zero. It turns out that if cable is made out of superconductor, it must be continuously cooled throughout. This would take several times more energy than the amount that would be transferred to a superconducting transmission line.
However, recently it became clear that everything can be done much easier. At the beginning of this century, physicists have described the effect of superconductivity that occurs in crystals of magnesium diboride (MgB2). This material becomes a superconductor at 40 K (-233.15 degrees Celsius). But this is the temperature that can be easily obtained by cooling the material with liquid hydrogen. In addition, magnesium diboride is easy to obtain on a commercial scale.
At the symposium in Potsdam an interesting idea was proposed: what if the scientists were to create the so-called hybrid cable? It would house the superconducting filaments of MgB2, and in the very middle there would be a cavity through which liquid hydrogen will be transported.
Thus, two birds can be killed with one stone. First, the liquid hydrogen will be able to cool the magnesium diboride to the desired temperature, and it will become a superconductor. Secondly, hydrogen is a promising fuel. Currently the main problem in using it is the high cost of production, since it consumes much more energy than the effect of using this gas is.
But factories for its production can be built in Sahara, where they would work on solar energy. Thus, the greatest desert of the Earth would be both the provider of alternative fuel and super cheap electricity. The stumbling block is a conductor.
Russian experts from the Institute of Microelectronics Nanotechnology, Russian Research, Design and Technological Institute of the cable industry and the Moscow Aviation Institute decided to implement this wonderful idea. They created a cable with the diameter of 26 millimeters with a cavity for the transportation of liquid hydrogen in the center (its diameter is 12 millimeters).
Outside of it is the current-carrying layer, consisting of five strips of magnesium diboride (produced by specialists from the Italian company Columbus Superconductor), spirally arranged on the core of a bundle of copper wires. In addition, the liquid hydrogen circulated in the cavity between the outer cable sheath and the inner wall of the cryostat. The length of the experimental cable was ten meters, which was sufficient for the first test.
Recently, this new product has been tested on a special stand of the Chemical Automation Design Bureau in the city of Voronezh. According to the test results, it became clear that it worked and the cooled magnesium diboride has shown the properties of a superconductor. According to a fellow of All-Russian Scientific Research of Design and Technology Institute of the Cable Industry Vitaly Vysotsky, the experiment showed that in this model the flow of liquid hydrogen at 200-220 g/s is able to carry approximately 25 megawatts of power. In parallel, approximately 50 megawatts of electricity was transmitted with the superconducting cable.
However, according to the scientists, this is not the limit. Vysotsky said that "the last indicator can be easily tripled by adding the number of superconducting tapes. At the industry scale by increasing the current, voltage and volume flow of hydrogen (which is solved by increasing the diameter of the pipe) a much more powerful energy flows can be transmitted." That is, the supposed power of ten gigawatts is not something fundamentally unattainable for this cable.
The Russian scientists have said that this experiment was very promising. It became clear that the creation of superconducting power transmission lines from inexpensive materials is possible in principle, even on the industrial scale. For Russia with its vast distances it is especially important, because the existing power structures will never be sufficient. The superconducting cables would solve the problem quickly and easily - just one or two plants would supply energy to all citizens of Russia, from Kaliningrad to Vladivostok.
Anton Evseev
Pravda.Ru
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http://english.pravda.ru/science/tech/26-03-2012/120888-hybrid_superconducting-0/
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[using microwave radiation in a resonating superconducting cavity and other emf to create resonating thrust due to strange properties of relativity; this is a prototype idea and the actual materials issues are problematic, though an interesting use of harnessing a force that most physicists attempt to demote in their constructive work, instead here it is enhanced:
"The key, says Shawyer, is to make the cavity superconducting. Without electrical resistance, currents in the cavity walls will not generate heat. Engineers in Germany working on the next generation of particle accelerators have achieved a Q of several billion using superconducting cavities. If Shawyer can match that performance, he calculates that the thrust from a microwave engine could be as high as 30,000 newtons per kilowatt - enough to lift a large car."]
Relativity drive: The end of wings and wheels?
08 September 2006
www.newscientisttech.com/article/mg19125681.400;jsessionid=NMGHKBGMCGMM
Justin Mullins
Web Links
Shawyer's theory paper (pdf)
Look, no wings! The trip from London to Havant on the south coast of England is like travelling through time. I sit in an air-conditioned train, on tracks first laid 150 years ago, passing roads that were known to the Romans. At one point, I pick out a canal boat, queues of cars and the trail from a high-flying jet - the evolution of mechanised travel in a single glance.
But evolution has a habit of springing surprises. Waiting at my destination is a man who would put an end to mechanised travel. Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete. "The end of wings and wheels" is how he puts it. It's a bold claim. Read Shawyer’s theory paper here (pdf format).
Of course, any crackpot can rough out plans for a warp drive. What they never show you is evidence that it works. Shawyer is different. He has built a working prototype to test his ideas, and as a respected spacecraft engineer he has persuaded the British government to fund his work. Now organisations from other parts of the world, including the US air force and the Chinese government, are beating a path to his tiny company.
The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation - microwaves to be precise - by exploiting the strange properties of relativity. It has no moving parts, and releases no exhaust or noxious emissions. Potentially, it could pack the punch of a rocket in a box the size of a suitcase. It could one day replace the engines on almost any spacecraft. More advanced versions might allow cars to lift from the ground and hover. It could even lead to aircraft that will not need wings at all. I can't help thinking that it sounds too good to be true.
When I meet Shawyer, he turns out to be reassuringly normal. His credentials are certainly impressive. He worked his way up through the aerospace industry, designing and building navigation and communications equipment for military and commercial satellites, before becoming a senior aerospace engineer at Matra Marconi Space (later part of EADS Astrium) in Portsmouth, near where he now lives. He was also a consultant to the Galileo project, Europe's satellite navigation system, which engineers are now testing in orbit and for which he negotiated the use of the radio frequencies it needed.
Dangerous idea
With that pedigree, you'd imagine Shawyer would be someone the space industry would have listened to. Far from it. While at Astrium, Shawyer proposed that the company develop his idea. "I was told in no uncertain terms to drop it," he says. "This came from the very top."
What Shawyer had in mind was a replacement for the small thrusters conventional satellites use to stay in orbit. The fuel they need makes up about half their launch weight, and also limits a satellite's life: once it runs out, the vehicle drifts out of position and must be replaced. Shawyer's engine, by contrast, would be propelled by microwaves generated from solar energy. The photovoltaic cells would eliminate the fuel, and with the launch weight halved, satellite manufacturers could send up two craft for the price of one, so you would only need half as many launches.
So why the problem? Shawyer argues that for companies investing billions in rockets and launch sites, a new technology that leads to fewer launches and longer-lasting satellites has little commercial appeal. By the same token, a company that offers more for less usually wins in the end, so Shawyer's idea may have been seen as too speculative. Whatever the reason, in 2000, he resigned to go it alone.
Surprisingly, Shawyer's disruptive technology rests on an idea that goes back more than a century. In 1871 the physicist James Clerk Maxwell worked out that light should exert a force on any surface it hits, like the wind on a sail. This so-called radiation pressure is extremely weak, though. Last year, a group called The Planetary Society attempted to launch a solar sail called Cosmos 1 into orbit. The sail had a surface area of about 600 square metres. Despite this large area, about the size of two tennis courts, its developers calculated that sunlight striking it would produce a force of 3 millinewtons, barely enough to lift a feather on the surface of the Earth. Still, it would be enough to accelerate a craft in the weightlessness of space, though unfortunately the sail was lost after launch. NASA is also interested in solar sails, but has never launched one. Perhaps that shouldn't be a surprise, as a few millinewtons isn't enough for serious work in space.
But what if you could amplify the effect? That's exactly the idea that Shawyer stumbled on in the 1970s while working for a British military technology company called Sperry Gyroscope. Shawyer's expertise is in microwaves, and when he was asked to come up with a gyroscopic device for a guidance system he instead came up with the idea for an electromagnetic engine. He even unearthed a 1950s paper by Alex Cullen, an electrical engineer at University College London, describing how electromagnetic energy might create a force. "It came to nothing at the time, but the idea stuck in my head," he says.
In his workshop, Shawyer explains how this led him to a way of producing thrust. For years he has explored ways to confine microwaves inside waveguides, hollow tubes that trap radiation and direct it along their length. Take a standard copper waveguide and close off both ends. Now create microwaves using a magnetron, a device found in every microwave oven. If you inject these microwaves into the cavity, the microwaves will bounce from one end of the cavity to the other. According to the principles outlined by Maxwell, this will produce a tiny force on the end walls. Now carefully match the size of the cavity to the wavelength of the microwaves and you create a chamber in which the microwaves resonate, allowing it to store large amounts of energy.
What's crucial here is the Q-value of the cavity - a measure of how well a vibrating system prevents its energy dissipating into heat, or how slowly the oscillations are damped down. For example, a pendulum swinging in air would have a high Q, while a pendulum immersed in oil would have a low one. If microwaves leak out of the cavity, the Q will be low. A cavity with a high Q-value can store large amounts of microwave energy with few losses, and this means the radiation will exert relatively large forces on the ends of the cavity. You might think the forces on the end walls will cancel each other out, but Shawyer worked out that with a suitably shaped resonant cavity, wider at one end than the other, the radiation pressure exerted by the microwaves at the wide end would be higher than at the narrow one.
Key is the fact that the diameter of a tubular cavity alters the path - and hence the effective velocity - of the microwaves travelling through it. Microwaves moving along a relatively wide tube follow a more or less uninterrupted path from end to end, while microwaves in a narrow tube move along it by reflecting off the walls. The narrower the tube gets, the more the microwaves get reflected and the slower their effective velocity along the tube becomes. Shawyer calculates the microwaves striking the end wall at the narrow end of his cavity will transfer less momentum to the cavity than those striking the wider end (see Diagram). The result is a net force that pushes the cavity in one direction. And that's it, Shawyer says.
Hang on a minute, though. If the cavity is to move, it must be pushed by something. A rocket engine, for example, is propelled by hot exhaust gases pushing on the rear of the rocket. How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in. Since the microwave photons in the waveguide are travelling close to the speed of light, any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity. This says that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.
"How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in"Each photon that a magnetron fires into the cavity creates an equal and opposite reaction - like the recoil force on a gun as it fires a bullet. With Shawyer's design, however, this force is minuscule compared with the forces generated in the resonant cavity, because the photons reflect back and forth up to 50,000 times. With each reflection, a reaction occurs between the cavity and the photon, each operating in its own frame of reference. This generates a tiny force, which for a powerful microwave beam confined in the cavity adds up to produce a perceptible thrust on the cavity itself.
Shawyer's calculations have not convinced everyone. Depending on who you talk to Shawyer is either a genius or a purveyor of snake oil. David Jefferies, a microwave engineer at the University of Surrey in the UK, is adamant that there is an error in Shawyer's thinking. "It's a load of bloody rubbish," he says. At the other end of the scale is Stepan Lucyszyn, a microwave engineer at Imperial College London. "I think it's outstanding science," he says. Marc Millis, the engineer behind NASA's programme to assess revolutionary propulsion technology accepts that the net forces inside the cavity will be unequal, but as for the thrust it generates, he wants to see the hard evidence before making a judgement.
Thrust from a box
Shawyer's electromagnetic drive - emdrive for short - consists in essence of a microwave generator attached to what looks like a large copper cake tin. It needs a power supply for the magnetron, but there are no moving parts and no fuel - just a cord to plug it into the mains. Various pipes add complexity, but they are just there to keep the chamber cool. And the device seems to work: by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power. Shawyer calculated that his first prototype had a Q of 5900. With his second thruster, he managed to raise the Q to 50,000 allowing it to generate a force of about 300 millinewtons - 100 times what Cosmos 1 could achieve. It's not enough for Earth-based use, but it's revolutionary for spacecraft.
One of the conditions of Shawyer's £250,000 funding from the UK's Department of Trade and Industry is that his research be independently reviewed, and he has been meticulous in cataloguing his work and in measuring the forces involved. "It's not easy because the forces are tiny compared to the weight of the equipment," he says.
Optimising the cavity is crucial, and it's as much art as science. Energy leaks out in all kinds of ways: microwaves heat the cavity, for example, changing its electrical characteristics so that it no longer resonates. At very high powers, microwaves can rip electrons out of the metal, causing sparks and a dramatic loss of power. "It can be a very fine balancing act," says Shawyer.
To review the project, the UK government hired John Spiller, an independent space engineer. He was impressed. He says the thruster's design is practical and could be adapted fairly easily to operate in space. He points out, though, that the drive needs to be developed further and tested by an independent group with its own equipment. "It certainly needs to be flown experimentally," he says.
Armed with his prototypes, the test measurements and Spiller's review, Shawyer is now presenting his design to the space industry. The reaction in China and the US has been markedly more enthusiastic than that in Europe. "The European Space Agency knows about it but has not shown any interest," he says. The US air force has already paid him a visit, and a Chinese company has attempted to buy the intellectual property associated with the thruster. This month, he will be travelling to both countries to visit interested parties, including NASA.
"A Chinese company has tried to buy rights to the microwave thruster"To space and beyond
His plan is to license the technology to a major player in the space industry who can adapt the design and send up a test satellite to prove that it works. If all goes to plan, Shawyer believes he could see the engine tested in space within two years. He estimates that his thruster could save the space industry $15 billion over the next 10 years. Spiller is more cautious. While the engine could certainly reduce the launch weight of a satellite, he doubts it will significantly increase its lifetime since other parts will still wear out. The space industry might not need to worry after all.
Meanwhile Shawyer is looking ahead to the next stage of his project. He wants to make the thrusters so powerful that they could make combustion engines obsolete, and that means addressing the big problem with conventional microwave cavities - the amount of energy they leak. The biggest losses come from currents induced in the metal walls by the microwaves, which generate heat when they encounter electrical resistance. This uses up energy stored in the cavity, reduces the Q, and the thrust generated by the engine drops.
Fortunately particle accelerators use microwave cavities too, so physicists have done a lot of work on reducing Q losses inside them. The key, says Shawyer, is to make the cavity superconducting. Without electrical resistance, currents in the cavity walls will not generate heat. Engineers in Germany working on the next generation of particle accelerators have achieved a Q of several billion using superconducting cavities. If Shawyer can match that performance, he calculates that the thrust from a microwave engine could be as high as 30,000 newtons per kilowatt - enough to lift a large car.
This raises another question. Why haven't physicists stumbled across the effect before? They have, says Shawyer, and they design their cavities to counter it. The forces inside the latest accelerator cavities are so large that they stretch the chambers like plasticine. To counteract this, engineers use piezoelectric actuators to squeeze the cavities back into shape. "I doubt they've ever thought of turning the force to other uses," he says.
No doubt his superconducting cavities will be hard to build, and Shawyer is realistic about the problems he is likely to meet. Particle accelerators made out of niobium become superconducting at the temperature of liquid helium - only a few degrees above absolute zero. That would be impractical for a motor, Shawyer believes, so he wants to find a material that superconducts at a slightly higher temperature, and use liquid hydrogen, which boils at 20 kelvin, as the coolant. Hydrogen could also power a fuel cell or turbine to generate electricity for the emdrive.
In the meantime, he wants to test the device with liquid nitrogen, which is easier to handle. It boils at 77 kelvin, a temperature that will require the latest generation of high-temperature ceramic superconductors. Shawyer hasn't yet settled on the exact material, but he admits that any ceramic will be tricky to incorporate into the design because of its fragility. It will have to be reliably bonded to the inside of a cavity and mustn't crack or flake when cooled. There are other problems too. The inside of the cavity will still be heated by the microwaves, and this will possibly quench the superconducting effect. "Nobody has done this kind of work," Shawyer says. "I'm not expecting it to be easy."
Then there is the issue of acceleration. Shawyer has calculated that as soon as the thruster starts to move, it will use up energy stored in the cavity, draining energy faster than it can be replaced. So while the thrust of a motionless emdrive is high, the faster the engine moves, the more the thrust falls. Shawyer now reckons the emdrive will be better suited to powering vehicles that hover rather than accelerate rapidly. A fan or turbine attached to the back of the vehicle could then be used to move it forward without friction. He hopes to demonstrate his first superconducting thruster within two years.
What of the impact of such a device? On my journey home I have plenty of time to speculate. No need for wheels, no friction. Shawyer suggested to me before I left that a hover car with an emdrive thruster cooled and powered by hydrogen could be a major factor in converting our society from a petrol-based one to one based on hydrogen. "You need something different to persuade people to make the switch. Perhaps being able to move in three dimensions rather than two would do the trick."
What about aircraft without wings? I'm aware that my feeling of scepticism is being replaced by a more dangerous one of unbounded optimism. In five minutes of blue-sky thinking you can dream up a dozen ways in which the emdrive could change the world. I have an hour ahead of me. The end of wings and wheels. Now there's a thought.
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http://www.newscientisttech.com/article/mg19125681.400;jsessionid=NMGHKBGMCGMM
Forget expensive liquid nitrogen. Room temperature superconductor materials created.
EE Times corrects story on silane as a potential superconductor
EE Times
(03/24/2008 8:00 PM EDT)
(Editor's note: A March 17 story about new research on the potential superconducting properties of the material silane contained numerous errors. They are corrected below.)
A Canadian-German research team has reported what they say is the first evidence that superconductivity can occur in a common gaseous hydrogen compound -- silane -- when compressed to a solid at very high pressure.
The finding, first published in the journal Science, promises to advance the design of more efficient superconducting materials that could be used for a variety of applications, the researchers said.
"Our research in this area is aimed at improving the critical temperature for superconductivity so that new superconductors can be operated at higher temperatures," said John Tse, Canada Research Chair in Materials Science at the University of Saskatchewan.
Tse carried out the theoretical work with doctoral candidate Yansun Yao using Canada's WestGrid computing facility. Experimental work was carried out by researcher Mikhail Eremets of the Max Planck Institute of Germany.
The new family of superconductors is based on a hydrogen-containing compound called silane, the silicon analog of methane. Silane combines a single silicon atom with four hydrogen atoms to form a molecular hydride. (Methane combines a single carbon atom with four hydrogen atoms.)
Researchers have long speculated that hydrogen under enough pressure would superconduct, but have so far been unable to achieve the necessary conditions since hydrogen is difficult to compress to the density required for superconductivity.
The Canadian and German researchers attributed their success to using a hydrogen-rich compound with silicon that reduced the amount of compression needed to achieve superconductivity.
In separate research, Tse's team is using the Canadian Light Source synchrotron to characterize the high-pressure structures of other hydrides as potential superconducting materials for industrial applications as well as a storage mechanism for hydrogen fuel cells.
The research was funded by the Natural Sciences and Engineering Research Council of Canada, the Canada Research Chairs program, the Canadian Foundation for Innovation and the Max Planck Institute.
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http://www.eetimes.com/news/latest/showArticle.jhtml;jsessionid=HTTOTGYXPCPWSQSNDLSCKHA?articleID=206904213
Superconductor breakthroughs abound: some like it hot
By Matt Ford | Published: April 20, 2008 - 03:19PM CT
Normally, big discoveries in a given field come at the rate of a few a year, if that. However, the past six weeks have seen not one, but a series of announcements that may change the face of superconductivity research.
Starting with a publication in the February 23rd edition of the Journal of the American Chemical Society and ending with three separate announcements from various Chinese research groups, these last few weeks have given us the description of a previously unknown class of high temperature superconductors.
When electrons flow through a conductor, they scatter due to thermal vibrations and material impurities—the amount of scattering is measured as the electrical resistance.
For most materials, as the temperature drops towards absolute zero, the electrical resistance asymptotically reaches the material's inherent conductivity.
However, once some materials drop below a critical temperature, the resistance drops to zero: these materials are known as superconductors. If one constructs a loop of superconducting material and sends an electric current moving through it, that current will persist for all time, since there is no resistance to stop it.
The current explanation for superconductivity is that conducting electrons form coordinated pairs that are inefficiently scattered; since conductance is inversely proportional to scattering, this leads to infinite conductance.
The temperature at which a material begins superconducting—the critical temperature—is very low.
Titanium will superconduct below 0.40 K; the figure for lead is all the way up at 7.19 K.
Some alloys are known to exhibit superconductivity at higher temperatures than pure compounds—Nb3Al has a critical temperature of 18.9 K.
According to the canonical explanation for superconductivity, [and canonical things have a tendency to blow up], the BCS theory, nothing should be able to exhibit superconductivity at a temperature above 30 K.
In 1986 this prediction was shown to be false with the discovery of the cuprate high temperature superconductors. The first, La1.15Ba0.85CuO, discovered in 1986 by Muller and Bednorz, was shown to have a critical temperature of 35 K.
The discovery was so ground breaking, it netted the pair the Nobel Prize in Physics the following year.
In the intervening 20 years, new materials in the cuprate high temperature superconductor family have been discovered.
Probably the most well known is the yttrium-barium-copper oxide (YBa2Cu3O7) which was the first superconducting material shown to superconduct at a temperature of 92 K, well above the boiling point of nitrogen.
The current record holder for high temperature superconductor is mercury thallium barium calcium copper oxide (Hg12Tl3Ba30Ca30Cu45O125) which transitions into superconductive state at a whopping 138 K—with some reports this can be raised to 164 K at high pressures.
However, these are still all well short of room temperature, 298 K.
Credit: Kamihara et al., JACS
Up until late February, all known high-temperature superconducting materials were some variation of a copper oxide.
In the month's final edition of JACS, a research team from the Tokyo Institute of Technology reported on the groundbreaking discovery of a lanthanum oxygen fluorine iron arsenide (LaO1-xFxFeAs)* that exhibits superconductivity at 26 K.
About a month later, researchers from the University of Science and Technology of China in Hefei announced that they had synthesized a samarium oxygen fluorine iron arsenide (SmO1-xFxFeAs)** ceramic that exhibited superconductivity at 43 K. Continuing the groundbreaking results, a second Chinese team, this one at the Institute of Physics (IoP) at the Chinese Academy of Sciences in Beijing, reported three days later that they had succeeded in creating praseodymium oxygen fluorine iron arsenide (PrO1-xFxFeAs)*** which had a critical temperature of 52 K. They made a second announcement a few weeks later, in which they reported that the superconducting temperature of their praseodymium compound could be raised to 55 K by growing it under pressure. [what if they grow it under pressure and under extreme cold, the cold hardening of metals is known...]
These four materials represent an entire new class of superconducting compounds, and their discovery could provide a big boost to our theoretical knowledge of superconductivity.
The field hasn't come to an agreement on to how to account for the behavior of cuprate high-temperature superconductors.
It is believed that the layered structure of the cuprates, the ability of electrons to hop from copper ion to copper ion, and the shielding provided by copper-free layers all contribute to the superconductivity. Since these new materials also have a similar-ish layered structure, are bad conductors before they transition, and exhibit antiferromagnetism, it is hoped that they can offer new insights into a general mechanism(s) of high-temperature superconductivity.
According to Steven Kivelson, a theoretical physicist at Stanford, "[there exist] enough similarities that it's a good working hypothesis that they're parts of the same thing."
However, not everyone hopes the mechanism is the same.
Philip Anderson, a Nobel Laureate and theoretical physicist at Princeton, says that an entirely new mechanism of superconductivity would be far more important than if they mimicked the current understanding of superconductivity.
"If it's really a new mechanism, God knows where it will go," says Anderson.
Further Reading:
* Found from Science magazine's ScienceNOW column
* arXiv list of papers by Prof. Chen
* arXiv list of papers by Prof. Zhao (IoP)
* J. Am. Chem. Soc., 2008. DOI: 10.1021/ja800073m
* x is in the range [0.05-0.12]
** x is one of 0, 0.05, 0.13, 0.3
*** x is 0.11
http://arstechnica.com/news.ars/post/20080420-superconductor-breakthroughs-abound-some-like-it-hot.html?rel
Superconducting wire:
High temperature superconductors, 20 years on
By John Timmer | Published: September 04, 2007 - 10:34AM CT
Back in 1987, the people who hand out Nobel Prizes recognized a major breakthrough: the development of non-metallic superconductors that carried electricity with no resistance at temperatures well above absolute zero. In honor of that event, Nature Materials is offering up an overview of the field. It has a couple of interviews with pioneers in the field (including one of the Nobel honorees), a review article, and a perspective on applications of these materials.
The review focuses on the challenges of making useful wiring out of exotic ceramics. A couple of commercial techniques have been developed, both based on a metal backbone coated with layers of material that ultimately pattern the superconductor that caps the structure. These wires are typically 4mm wide, with a superconducting layer that's over a micrometer thick.
The process of creating these wires is expensive, so an obvious route to reducing their costs is to have each one carry more power. This is where the actual physics of the superconducting process comes in. When carrying power, small magnetic vortices appear within the superconductors, induced by the current itself. At low power densities, these vortices remain anchored at defects in the superconducting material. But, once a critical amount of current is reached, the magnetic vortices begin to move, creating resistance and causing a rapid failure of the superconduction.
Increasing the current capacity of these wires becomes a balancing act. Researchers have found a number of ways to introduce defects in the material in a way that helps pin the magnetic flux in place, increasing the currents that can be carried. Unfortunately, it becomes harder to control the formation of defects as the layer of superconductor becomes thicker; adding thickness to the layer of superconductor is, of course, the obvious way to increase the current capacity of these wires. The remainder of the review focuses on different ways of balancing this trade-off, and ends with a call for a standardized testing regime, so that future work can be better integrated into a coherent picture.
The perspective focuses on the use of superconducting wires in real-world applications. It notes that electricity grids lose about 7-10 percent of their power through leakage and resistance, [in conventional non-superconducting wires] and most of that's not going away: the cooling needs for high-temperature superconductors prevent their use for anything beyond urban areas and power distribution centers, where wiring is very high density.
Currently, the US Department of Energy has funded test installations of superconducting cables up to 600m long at a number of power distribution centers.
The review estimates that superconducting wire will have to drop anywhere from a half to a third in price and double its current capacity before its installation becomes competitive with traditional wiring.
Meanwhile, the DOE is sponsoring efforts intended to reduce refrigeration costs by a quarter in order to cut down on operating costs.
Nothing, in theory, prevents any of these advances, but progress has been slow so far.
In the meantime, the review points out some uses that may make sense in the short term. The article notes that strategic placement of superconducting cabling can prevent the propagation of current spikes, such as the one that ["officially" was claimed to have] caused the northeast blackout in 2003.
As noted above, when a critical current density is surpassed, superconducting wires would simply stop superconducting, preventing these sorts of surges from spilling over to other areas of the grid.
The US Navy is also funding the development of superconducting electrical generators, which cut power losses in half, weigh a third less, and are far more compact when compared to traditional generators.
Given military budgets and the space requirements of ships, these seem to be a sensible trade off.
The perspective wraps up by indicating that we're still a number of years away from high-temperature superconductors making the transition from government-supported test cases to a profitable commercial industry.
That transition will also require funding for fields that aren't directly related to superconduction, such as the cryogenic technology needed to efficiently cool the installations.
Ultimately, its author (who works for one of the companies hoping to profit from the transition) hopes the government doesn't lose sight of the need for continued support during the remaining years needed for this transition to take place.
Nature Materials, 2007. DOI: 10.1038/nmat1989
Nature Materials, 2007. DOI: 10.1038/nmat1990
Buzz up!
Filed under: high-temperature superconductors, superconduction, materials science, physics, sciencemore...
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sidb
quote:
when a critical current density is surpassed, superconducting wires would simply stop superconducting
When an overloaded superconductor becomes resistive, wouldn't it overheat and sustain damage? Surely there's a more cost-efficient way to prevent spikes than using the electrical infrastructure as a giant fuse.
September 04, 2007 @ 12:39PM
Doomlord_uk
Nobel honorees are more commonly referred to as Nobel Laureates Smile
Interesting article.
September 04, 2007 @ 01:49PM
mto
I'm with SIDB
quote:
when a critical current density is surpassed, superconducting wires would simply stop superconducting
[sarcasm] This sounds a lot like a piece of technology known to electricians as a "fuse" or if you want to get fancy a "fusable link". Only now [with this idea of superconducting infrastructure] your fuse costs tens thousands of dollars and will do thousands of dollars of damage to supporting infrastructure when it flash boils some nitrogen.
September 04, 2007 @ 08:12PM
Fok
When the line quenches (the actual term for spontaneous loss of superconductivity) it doesn't have to do any damage. (ie, it doesn't get so hot as to destroy itself, or the cyrogen pressure doesn't get so high as to cause explosions.) Presumably, this would be the designed in case here.
Frankly though, I predict their use in the power grid will become common around the same time the first commercial fusion plant comes online. Which is perpetually 10 years out.
September 04, 2007 @ 08:39PM
Kalkin
+++ Surely all of these will be designed using flexible organic displays, and provide power for the flying cars that will follow. Razz
September 04, 2007 @ 11:59PM
Tsudo
http://en.wikipedia.org/wiki/Fault_Current_Limiters
Using superconductors to limit fault currents is an active area of interest...
September 05, 2007 @ 05:23AM
logicnazi
Does it matter if it damages the superconductor? It is still functioning as a massive surge protector.
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http://arstechnica.com/journals/science.ars/2007/09/04/high-temperature-superconductors-20-years-on?rel
[removing a superconducting requirement in lasers]
Room-temperature terahertz laser invented
R. Colin Johnson
(05/21/2008 12:07 PM EDT)
URL: http://www.eetimes.com/showArticle.jhtml?articleID=207801578
PORTLAND, Ore. — What's claimed to be the world's first room-temperature terahertz laser harnesses the optical equivalent of heterodyning to bridge the terahertz gap. Today, a terahertz-gap exists where most semiconductor lasers fail to operate--between microwave wavelengths (centimeters) and optical wavelengths (microns). In between are the millimeter wavelengths--terahertz frequencies (1-10 THz).
The only semiconductor lasers that run at terahertz frequencies today are supercooled quantum cascade lasers (QCL). Now, the co-inventor of the QCL (while at Bell Labs in 1994), professor Federico Capasso at Harvard University, has demonstrated a heterodyning method cast in nonlinear materials that mixes two easy-to-generate optical frequencies spaced apart at the desired terahertz frequency, resulting in a room-temperature terahertz laser.
"This class of nonlinear optical materials has the interesting property that, when illuminated by two frequencies, their constituent molecules vibrate coherently, not only at the driving frequencies, known as 'pump' frequencies, but also at their difference frequency," said Harvard professor, Federico Capasso. "As a result, at the output of the material one not only observes light at the pump frequencies, but also at the difference frequency--a process similar to the heterodyne principle widely used in radio."
By choosing optical wavelengths that are easy to generate at room temperature--but whose difference is exactly the desired terahertz frequency--Capasso and Harvard research associate Mikhail Belkin sidestepped the terahertz-gap problem, resulting in a terahertz laser that operates at room temperature. The two optical lasers used by Capasso's group in its room-temperature demonstration were at 33.7-THz (8.9-micron wavelength) and 28.5-THz (10.5-micron wavelength), which produced a difference frequency of 5.2 THz.
"Basically, electrons are driven to oscillate all in phase at this frequency, thus producing coherent terahertz emission," said Capasso. "The device structure is both a two frequency mid-infrared QCL and a nonlinear material, which generates the frequency difference. Since the two mid-infrared frequencies are generated at room temperature, their difference obviously is, as well. In this way we have circumvented the limitation of THz QCLs, which operate so far only at cryogenic temperatures."
Terahertz scanners act like x-rays, but at power levels that are completely safe to use around people. Using a terahertz scanner, airports could detect hidden weapons under clothing, as well as hazardous and toxic materials inside luggage. Terahertz lasers could also remotely detect hazardous gases floating in the air, offering a potential solution to identifying improvised explosive devices from a distance.
Conventional lasers energize electrons, which then emit a single photon by jumping from the semiconductor's conduction band to its valence band. Quantum cascade lasers, on the other hand, arrange a stair-step of quantum wells--each at a progressively lower energy level--that allow electrons to cascade down an energy staircase, emitting a photon at each step. Today, quantum cascade lasers lose their ability to work in the terahertz gap without supercooling. But by using a heterodyning architecture, the Harvard researchers demonstrated twin quantum cascade lasers, whose mixed output is in the terahertz gap.
The heterodyning principle is well known in nonlinear optics as difference frequency generation (DFG). Most materials act like linear harmonic oscillators when light impinges on them, oscillating only when the frequency matches their own internal natural resonant frequency. Nonlinear materials like vacuum tubes and transistors, on the other hand, can be made to resonate at the sum and difference frequencies of two inputs, enabling radios to move signals between bands, or to encode and decode them.
Others have demonstrated the feasibility of terahertz lasers using DFG, but bulky external "pump" lasers were used just to prove the principle. The Harvard group accomplished the task with semiconductor materials that, if all goes well, eventually could be mass produced for inexpensive room-temperature devices.
"Our device does everything in one small semiconductor crystal with no need for bulky external lasers for pumping; hence, the advantages of compactness, portability and low power consumption," said Capasso. "In essence, the material of the device is designed and grown so that when a bias current is applied to it, not only are laser beams emitting at two different mid-infrared frequencies generated, but also coherent radiation at the difference frequency corresponding, in our case, to 5 Terahertz".
The mechanism by which nonlinear devices perform operations like mixing--generating sum and difference frequencies--depends on the materials used. The quantum cascade laser is fabricated using molecular-beam epitaxy, a layer of atoms at a time, from alternating layers of gallium and aluminum. Each layer is slightly thinner than the one before it.
Next, the Harvard researchers plan to optimize their design in an attempt to increase the output power to milliwatts, from its nanowatt levels today. One way is to add low-cost thermoelectric coolers to the laser's substrate--since the cooler the laser runs, the higher its output power. Secondly, the group plans to switch from edge emission to surface emission for their semiconductor material.
"Our approach will be to greatly increase the surface area used for emission," said Capasso. "Surface emission will be achieved by fabricating a suitable grating to scatter vertically the terahertz radiation generated in the device's active region."
Belkin and Capasso performed the work in cooperation with researchers Feng Xie and Alexey Belyanin, at Texas A&M University (College Station), and researchers Milan Fischer, Andreas Wittmann, and Jrme Faist, at ETH (Zurich, Switzerland). Funding was provided by the Air Force Office of Scientific Research, the National Science Foundation and two Harvard-based centers, the Nanoscale Science and Engineering Center and the Center for Nanoscale Systems, a member of the National Nanotechnology Infrastructure Network.
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http://www.eetimes.com/news/latest/showArticle.jhtml;jsessionid=JOLB0PMQ2C2GQQSNDLPCKH0CJUNN2JVN?articleID=207801578
[more electric wire, and transparent superconductors as well]
Room Temperature Superconductors, Inc.
Has developed what are believed to be the world’s first, commercial, ambient-temperature superconducting polymer materials, trademarked Ultraconductors
RTS has three issued U.S. Patents.
The very large
pending application is in the process of division. It will become ten additional patent applications.
To read more about this exciting technology
Click here
Room Temperature Superconductors Inc. (RTS),
a subsidiary of Magnetic Power Inc., has developed the world's first ambient temperature superconducting materials, trademarked Ultraconductors. The company has worldwide rights to this technology, with landmark process and materials patents U.S. #5,777,292 and #6,552,883.
RTS also has achieved significant polymer technology breakthroughs and experimental demonstrations for film applications, enhanced materials properties, and additional superconducting materials.
The company's primary technology objectives are:
* To develop commercial processes and core fabrication technologies
* To reach application-ready platforms for commercial film and wire products
* To achieve proof of concepts for additional product applications
WHAT is an Ultraconductor ?
Ultraconductors
- A Primer -
By Kevin P. Shambrook, Ph.D.
ULTRACONDUCTORtm n. "Electrical conductors, which have certain properties similar to present-day superconductors. They are best considered as a novel state of matter."
Ultraconductors are patented materials being developed for commercial applications by Room Temperature Superconductors, Inc. They are made by the sequential processing of amorphous polar dielectric elastomers.
They exhibit a set of anomalous magnetic and electric properties, including: very high electrical conductivity (> 1011 S/cm -1) and current densities (> 5 x 108 A/cm2) over a wide temperature range (1.8 to 700 K).
Additional properties established by experimental measurements include: the absence of measurable heat generation under high current; thermal versus electrical conductivity orders of magnitude in violation of the Wiedemann-Franz law; a jump-like transition to a resistive state at a critical current; a nearly zero Seebek coefficient over the temperature range 87 - 233 K; no measurable resistance when Ultraconductor(tm) films are placed between superconducting tin electrodes at cryogenic temperatures.
The Ultraconductor properties are measured in discrete macromolecular structures which form over time after the processing.
In present thin films (1 - 100 micron) these structures, called 'channels', are typically 1 - 2 microns in diameter, 10 - 1000 microns apart, and are strongly anisotropic in the Z axis.
RTS was founded in 1993 to develop the Ultraconductor(tm) technology, following 16 years of research by a scientific team at the Polymer Institute, Russian Academy of Sciences, led by Dr. Leonid Grigorov, Ph.D., Dc.S. There have been numerous papers in peer-reviewed literature, 4 contracts from the U.S. government, a landmark patent (US patent # 5,777,292). and a devices patent (US patent # 6,552,883.)
Another patent is pending and a fourth now is being completed.
To date 7 chemically distinct polymers have been used to create Ultraconductors(tm), including olefin, acrylate, urethane and silicone based plastics. The total list of candidate polymers suited to the process is believed to number in the hundreds.
In films, these channels can be observed by several methods, including phase contrast optical microscope, Atomic Force Microscope (AFM), magnetic balance, and simple electric contact. The channel structures can be moved and manipulated in the polymer.
Ultraconductor(tm) films may be prepared on metal, glass, or semiconductor substrates.
The polymer is initially viscose (during processing). For practical application the channels may be "locked" in the polymer, by crosslinking, or glass transition.
The channel's characteristics are not affected by either mode.
A physics model of the conducting structures, which fits well with the experimental measurements, and also a published theory, have been developed. The next step in material development is to increase the percentage or "concentration" of conducting material.
This will lead to films with a larger number of conducting points (needed for interposers and other applications) and to wire.
Wire is essentially extending a channel to indefinite length, and the technique has been demonstrated in principle. Connecting to these conducting structures is done with a metal electrode, and when two channels are brought together they connect.
From an engineering point of view, we expect the polymer to replace copper wire and HTS in many applications.
It will be considerably lighter than copper, and have less electric resistance.
---
http://www.ultraconductors.com/primer.html
Ultraconductors are the result of more than sixteen years of prior scientific research, peer reviewed publication, independent laboratory testing, and eight years of engineering development.
From an engineering perspective, Ultraconductors are a fundamentally new and enabling technology. They are lightweight, flexible, transparent, and possess magnetic, electric, and electronic properties of exceptionally high commercial value.
Ultimately, Ultraconductors will offer unprecedented high performance and energy efficiency throughout a very broad range of products.
These applications will include:
* Electric power products (Power downleads, motors, generators, transmission lines)
* Electronics (microelectronic circuits and components, computer chip mounting, antennas)
* Medical (MRI systems, sensors, specialized instruments)
* Electromagnetics (energy storage, shielding)
More PDF documents from them here:
http://ultraconductors.com/documents.html
Ideally in a commodity ecology, only superconductors exist for power transmission.
31 May 2007
Tantalizing Hint Of Room-Temperature Superconductor
by Kate Melville
Tiny, isolated patches of superconductivity exist within certain ceramics at higher temperatures than previously thought possible, according to a report by Princeton scientists in Nature. The researchers say their findings were made possible by new techniques to image superconducting behavior at the nanoscale, producing "maps" of superconductivity in various materials.
Room-temperature superconductivity could revolutionize power transmission and open up a whole plethora of "green" options for energy transfer and storage. Unfortunately, researchers have not been able to move beyond the "high-temperature" ceramic superconductors discovered two decades ago that must be cooled to more than minus 100 degrees Celsius. Now, however, thanks to a special customized microscope, superconductivity temperatures may start to move upward.
The Princeton team's souped-up scanning tunneling microscope allowed them to identify traces of superconductivity that remain present inside ceramic superconductors even when they are warmed up above the critical temperature where they lose their resistance. Though the entire sample is too warm to exhibit superconductivity, disconnected regions within it possess Cooper pairs - coupled electrons that carry current through a superconductor - which previously were only known to appear below the critical temperature at which a material superconducts.
(Image above shows red areas indicating the presence of superconducting pairs. Even at 10 degrees Celsius above Tc, the temperature at which the entire sample exhibits superconductivity, the electron pairs still exist in localized regions).
While the regions are tiny - only a few nanometers wide - they appear in some materials at up to 50 degrees above the critical temperature. Researcher Ali Yazdani said that understanding why these minuscule patches of superconductivity exist at higher temperatures - and how to create a material that exhibits the property everywhere - may be the key to enhancing superconductivity.
"Our measurements show that Cooper pairs survive in local patches of the material at temperatures far above the critical temperature," said Yazdani. "Within these tiny regions, there are particular arrangements of atoms that favor formation of electron pairs at very high temperatures."
The research team says that electron pairing is a function of highly localized chemistry in the sample, often in patches only a few atoms wide. "If we can figure out the details of what is happening at these local patches within the samples, it might be possible to construct a material that performs better overall," said Yazdani.
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http://www.scienceagogo.com/news/20070430202007data_trunc_sys.shtml
17 August 2006
Magnetic Field Creates Bizarre Superconducting Effects
by Kate Melville
Powerful magnetic fields appear to change the physical nature of superconductivity with some quite bizarre effects, according to University of Arizona (UA) physicist Andrei Lebed. Lebed says that strong magnetism changes the basic properties of electrons flowing through superconductors, establishing an "exotic" superconductivity.
If his theorem can be proved via experiment, it will advance our knowledge of superconductivity considerably and open up a number of exciting new areas of research.
Since Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in 1911, scientists have steadily been uncovering the workings of superconductivity.
In 1957, physicists John Bardeen, Leon Cooper and Robert Schrieffer proposed a comprehensive theory to explain the behavior of superconducting materials.
The theory, called "BCS theory," was the first great insight into superconductivity. The work garnered them the 1972 Nobel Prize in Physics.
What this triumvirate of researchers had discovered is that electrons in a superconductor don't act as individual particles, but as pairs, now known as "Cooper pairs."
When electrical voltage is applied to a superconductor, all Cooper pairs move as a single entity, establishing an electrical current.
This normally works only at very low temperatures. When the superconductor warms up, its Cooper pairs separate into individual electrons and the material becomes a normal non-superconductor.
"People always have thought about the Cooper pair as behaving as an elementary particle, which is characterized by size, electric charge, spin, mirror-reflection and time-reversal properties," Lebed explained. But contrary to this commonly held theory, Lebed has shown that superconducting electron pairs are not unchanged elementary particles, but rather complex objects with characteristics that depend on the strength of the magnetic field that they are exposed to.
Lebed's theorem flies in the face of theoretical and experimental studies of rotating Cooper pairs in helium-3. Electrons in such Cooper pairs are believed to have either conventional "singlet" or unconventional "triplet" internal rotation (spin). When the spins of the two electrons are in opposite directions, one spinning up and the other spinning down, they are called singlets, or non-rotating Cooper pairs. When the spins are in same direction, they are called triplets, or rotating Cooper pairs.
But Lebed says that super-strong magnetic fields create exotic Cooper pairs that behave according to the weird, non-intuitive laws of quantum mechanics: the electron pairs are both rotating and non-rotating at the same time.
And that's not the only strange effect that the magnetic field can have. Because Cooper pairs are quantum objects, they behave both as particles and as standing waves.
One standing wave property is mirror reflection, or "parity."
Conventional superconductor theory states that wave symmetry in conventional, or singlet, superconductors is even. It is mathematically termed as 1. Unconventional, or triplet, superconductor parity is odd, or -1. When singlets or triplets are reflected in a mirror, the reflected waves always have the same ( 1) or opposite (-1) parity of the original waves.
Lebed however, finds that in strong magnetic fields, Cooper pair wave symmetries break down and the reflected waves don't look like the original waves. "It's like the Cooper pair wave sees someone else in the mirror," he said. "It's like Alice's adventure in a super-wonderland, where the mirrors are unusual and wrong. Because these Cooper pair electrons behave so differently than conventional singlet and unconventional triplet Cooper pairs, we call them 'exotic' Cooper pairs," he added.
Other effects of exotic superconducting phases indicate that time-reversal symmetry breaks down in exotic Cooper pairs.
"This is the most fundamental symmetry in physics and breaks down only in some rare processes in high energy, or elementary particle, physics," Lebed explained. He and co-researcher Omjyoti Dutta say that time-reversal symmetry is broken because of the simultaneous rotating and non-rotating average spins of exotic Cooper pairs.
"Half of the exotic Cooper pair electrons 'see' time directed from the past to the future, whereas the other half 'see' time directed from the future to the past," Lebed said.
Lebed offers the caveat that his theoretical results are very general. "They are based on a mathematical theorem and have to be experimentally applied to most kinds of existing superconducting materials, including high-temperature superconductors."
To that end, he and his co-researchers are designing simple experiments for observing exotic superconductivity and its attendant effects.
Source: University of Arizona Communications
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http://www.scienceagogo.com/news/20060717005040data_trunc_sys.shtml
19 October 2006
Magnetic Appeal Of Schizophrenic Superconductors
by Kate Melville
Researchers believe they have developed a theory to explain how ultra-narrow wires (nanowires) show enhanced superconductivity when exposed to strong magnetic fields.
The new theory, applying to wires only a few hundred atoms across, appears in Physical Review Letters.
Magnetic fields are something of an enigma when it comes to superconductors. Generally, magnetic fields suppress a material's ability to exhibit superconductivity, but under some conditions, a magnetic field can actually boost superconductivity.
Until now, there has been no satisfactory explanation for these sorts of behaviors.
"This phenomenon [of magnetic fields boosting superconductivity] is indeed curious," said researcher Alexey Bezryadin, given that magnetic fields have long been known to suppress superconductivity by raising the kinetic energy of the electrons and by influencing electron spin. Additionally, magnetic atoms, if present in the wires, also inhibit superconductivity.
But research by another scientist, Paul Goldbart, suggested that the enhancement observed by Bezyradin's group was due to magnetic moments in the wires. "Even though the two effects - magnetic fields and magnetic moments - work separately to diminish superconductivity; together one effect weakens the other, leading to an enhancement of the superconducting properties," Goldbart explained.
Working together, Bezryadin and Goldbart proposed that exposure of the wires to oxygen in the atmosphere causes magnetic moments to form on the wire surfaces. On their own, the moments weaken the superconductivity, but the magnetic field inhibits their ability to do this. This effect shows up in ultra-narrow wires because so many of their atoms lie near the surface, where the magnetic moments form.
"The results of this work may provide a key to explaining our previous findings that nanowires undergo an abrupt transition from superconductor to insulator as they get smaller," said Bezryadin.
Related Articles:
Magnetic Field Creates Bizarre Superconducting Effects
New Type Of Superconductor Emerges
Source: University of Illinois at Urbana-Champaign
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http://www.scienceagogo.com/news/20060919051047data_trunc_sys.shtml
1 April 2005
New Type Of Superconductor Emerges
by Kate Melville
University of California scientists and researchers from Chonnam National University in South Korea have found that magnetic fluctuations appear to be responsible for superconductivity in a compound called plutonium-cobalt-pentagallium (PuCoGa5). The discovery of this "unconventional superconductivity" may lead scientists to a whole new class of superconducting materials and toward the goal of creating superconductors that operate at room-temperature.
The research report, appearing in Nature, details how magnetic fluctuations, rather than interactions mediated by tiny vibrations in the underlying crystal structure, may be responsible for the electron pairing that produces superconductivity in this particular mixture of plutonium, cobalt and gallium.
Since the discovery at Los Alamos of PuCoGa5 roughly two years ago, the big question has been whether the compound was just another garden-variety superconductor (a s-wave superconductor), or an unconventional one that is mediated by magnetic fluctuations (a d-wave superconductor).
Although the temperatures at which superconductivity is observed are usually quite low, a handful of compounds like PuCoGa5 have been found to possess superconductivity at temperatures warmer than minus 427 degrees Fahrenheit.
Even though that temperature seems low, PuCoGa5 possesses highest superconducting transition temperature among actinide based compounds found so far. This "unconventional superconductivity" suggests that PuCoGa5 may be one of a very small handful of superconductors whose superconductivity actually derives from magnetic correlations.
Scientists theorize that having found one unconventional superconductor like PuCoGa5, they may find more in the future.
Making the research even more intriguing is the fact that plutonium is a base actinide material of the compound.
This new class of magnetically mediated superconductors might encompass a broad range of materials, metals to oxides, and be the path toward superconductor science's ultimate goal to someday synthesize a "room-temperature" superconductor that would be the basis for the dissipation-less flow of electric current through power lines, and for an even more efficient generation of computer semi-conductors.
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http://www.scienceagogo.com/news/20050231213016data_trunc_sys.shtml
27 March 2006
Not So Fast Einstein!
by Kate Melville
A quantum theory of gravity could be within reach, as scientists funded by the European Space Agency (ESA) report measuring the gravitational equivalent of a magnetic field. Presenting their results at a one-day conference at ESA's European Space and Technology Research Center (ESTEC) in the Netherlands earlier this month, the scientists involved said that under special conditions the gravitational effect was far greater than expected, and therefore contradicted Einstein's Theory of General Relativity that states such gravitational effects should be negligible.
Moving electrical charges and objects create magnetic and gravitomagnetic fields respectively, but Einstein claimed that the effect of the latter would be barely perceptible. Not so, says researcher Martin Tajmar and his colleagues, who believe that the effects of gravitomagnetic fields could explain the anomalies seen in high-precision mass measurements of Cooper-pairs (carriers in superconductors) and their prediction via quantum theory.
The team conducted an experiment using a ring of superconducting material that rotates at approximately 6,500 RPM. It has already been observed that rotating superconductors emit a weak magnetic field, known as a London moment, but Tajmar says that his team have also detected a gravitomagnetic field.
The team detected what has been dubbed the "Gravitomagnetic London Moment" by placing small acceleration sensors at various locations close to the spinning superconductor. Once the superconductor has reached a particular speed, claim the team, the sensors pick up an acceleration field outside the superconductor that appears to be produced by gravitomagnetism.
"This experiment is the gravitational analogue of Faraday's electromagnetic induction experiment in 1831. It demonstrates that a superconductive gyroscope is capable of generating a powerful gravitomagnetic field, and is therefore the gravitational counterpart of the magnetic coil. Depending on further confirmation, this effect could form the basis for a new technological domain, which would have numerous applications in space and other high-tech sectors," says researcher Clovis de Matos.
While 100 millionths of the acceleration due to Earth's gravitational field may not seem particularly astounding, the Gravitomagnetic London Moment detected by the team is a staggering one hundred million trillion times larger than what Einstein's Theory of General Relativity predicts. The results were so astonishing that the team did not believe the results themselves, but it soon turned out that the inconceivable had entered the realms of reality. "We ran more than 250 experiments, improved the facility over 3 years and discussed the validity of the results for 8 months before making this announcement. Now we are confident about the measurement," says Tajmar, who hopes that other scientists will now repeat his team's experiment to verify the results.
In addition to the team's experimental results, Tajmar has spent some time fine-tuning the theoretical aspects of the Gravitomagnetic London Moment. When the team used equations that allowed for force carrying particles (gravitons) to gain mass, they found that the gravitomagnetic force could be modeled. "If confirmed, this would be a major breakthrough," says Tajmar, "it opens up a new means of investigating general relativity and its consequences in the quantum world."
Source: European Space Agency
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http://www.scienceagogo.com/news/20060227023503data_trunc_sys.shtml
Public release date: 28-Nov-2001
Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
Superconductors that work at room temperature
TINY tubes of carbon may conduct electricity without any resistance, at temperatures stretching up past the boiling point of water.
The tubes would be the first superconductors to work at room temperature.
Guo-meng Zhao and Yong Sheng Wang of the University of Houston in Texas found subtle signs of superconductivity.
It wasn't zero resistance, but it's the closest anyone's got so far. "I think all the experimental results are consistent with superconductivity," Zhao says. "But I cannot rule out other explanations."
At the moment [that was 2001 this is untrue in 2008] no superconductor will work above about 130 kelvin (-143 ¡C). But if a material could carry current with no resistance at room temperature, no energy would be lost as heat, meaning faster, lower-power electronics. And electricity could be carried long distances with 100 per cent efficiency.
Zhao and Wang studied the effects of magnetic fields on hollow fibres of carbon known as "multiwall carbon nanotubes". Each nanotube is typically a millionth of a metre long, several billionths of a metre in diameter and with walls a few atoms thick. The nanotubes cling together in oblong bundles about a millimetre in length.
The researchers did not see zero resistance in their bundles. They think this is because the connections between the tiny tubes never become superconducting. But they did see more subtle signs of superconductivity within the tubes themselves.
For example, when the researchers put a magnetic field across a bundle at temperatures up to 400 kelvin (127 ¡C), the bundle generated its own weak, opposing magnetic field. Such a reaction can be a sign of superconductivity. And when the team cooled the bundles from even higher temperatures then turned the external field off, they stayed magnetised. A current running around within the tubes could generate this lingering field if there wasn't any resistance to make it fade away.
While each effect could have a more prosaic explanation, they varied in similar ways as the temperature of the bundles changed. The correlation suggests superconductivity was responsible, Zhao and Wang argue in a paper to be published in Philosophical Magazine B. However, their argument doesn't convince Paul Grant, a physicist with the Electric Power Research Institute in Palo Alto, California. "Generally, superconductivity is such a dominating effect [if there is just one mechanism which fails to be the case it seems] that when it occurs it just shouts out at you," Grant says. "It doesn't appear in these indirect ways."
Superconductivity theories do not forbid the phenomenon at very high temperatures, says Sasha Alexandrov, a theoretical physicist at Britain's Loughborough University.
A material becomes superconducting when its electrons pair up.
Normally such negatively charged particles would repel each other, but in a positively charged crystal structure, vibrations called phonons help them get together.
In carbon nanotubes, the frequency of these vibrations is very high, which, in theory at least, means superconductivity at higher temperatures. "The results on the magnetic response are very intriguing, and favour the explanation they present," Alexandrov says. "It's certainly possible," agrees David Caplin, head of the Centre for High Temperature Superconductivity at Imperial College, London.
To decide whether or not the nanotubes really are superconductors, you need to measure the resistance through a single tube, Alexandrov says. "To be convinced, I'd like to see zero resistance."
###
Author: Adrian Cho More at: www.arxiv.org/abs/cond-mat/0111268
New Scientist issue: 1st December 2001
PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: www.newscientist.com
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http://www.eurekalert.org/pub_releases/2001-11/ns-stw112801.php
newscientist.com/daily news.jsp?id=ns9999562
A New Superconductor said to have Zero Electrical Resistance at Room Temperature is Revealed but Scepticism Remains
Superconductivity is creating a buzz again with the announcement of a new material that is said to have zero electrical resistance at room temperature.
The claim, from researchers in Croatia, comes just a few weeks after the discovery that the simple chemical magnesium diboride superconducts at temperatures up to almost twice those needed for other metallic superconductors to work.
The Croatian scientists say that current will flow effortlessly through their material, a mixture of lead carbonate and lead and silver oxides, at up to about 30 °C.
"These results are suggestive of a transition to a superconducting state," says Georg Bednorz of the IBM Zurich Research Laboratory, who shared the 1987 Nobel physics prize for discovering cuprate superconductors.
But because of numerous false alarms in this field, researchers are treating the announcement with caution, especially as no one has yet managed to reproduce the results.
Magic formula
Danijel Djurek, a physicist at A. Volta Applied Ceramics in Zagreb, Croatia, claims that he discovered his superconducting ceramic mixture in the late 1980s. But he was unable to pin down the structure and formula of the material, and his research was interrupted by years of war, following Croatia's split from Yugoslavia.
Now Djurek and his team say they have finally hit on a formula that works reliably and reproducibly at room temperature.
Some telltale signs of superconductivity are easy to spot.
For example, a graph of resistance plotted against temperature shows a characteristic drop at the temperature at which the material becomes superconducting. Physicists usually require other evidence too, such as the ability to expel all magnetic fields. Djurek's material seems to do this too.
Archie Campbell, director of Cambridge University's Interdisciplinary Research Centre in Superconductivity, says the data clearly shows the hallmark of a superconductor. "This is not a small effect. There's no room for misinterpretation," he says, adding it's either superconductivity or it's a mistake.
Nevertheless, all the researchers contacted by New Scientist were extremely reluctant to start popping corks. "I have some concerns which keep my enthusiasm on a moderate level," says Bednorz.
Do it again
The biggest question mark hangs over the failure of other groups to replicate the results. Paul Chu, director of the Texas Center for Superconductivity at the University of Houston, has been following Djurek's work for some time.
"We recently tried to use his new formula but failed to reproduce his results," says Chu. "I think we will try a little more. It's too important to ignore."
German Patent # 10007915
Material used, e.g., in the Production of a Sputtering Target and as a Superconductor contains Lead, Carbon and Oxygen
Danijel Djurek. et al.
Patent number: DE10007915
Publication date: 2001-09-13
Inventor: DJUREK DANIJEL (HR); MEDUNIC ZVONKO (HR); PALJEVIC MATIJA (HR); TONEJC ANTON (HR)
Applicant: ALCATEL HIGH TEMPERATURE SUPER (DE)
Classification: --- International: C22C11/00; C22C32/00; H01L39/12; C22C11/00; C22C32/00; H01L39/12; (IPC1-7): H01B12/00; C22C5/06; C22C11/00; G01R33/035; H01B1/02; H01B12/10; H01F6/00; H01F27/28; H02K3/02; ---- European: C22C11/00; C22C32/00; H01L39/12C
Application number: DE20001007915 20000221
Priority number(s): DE20001007915 20000221
Abstract: Material contains at least 5 wt.% lead, at least 0.1 wt.% carbon and at least 1 wt.% oxygen and has a specific electrical resistance of not more than 0.5 x 10<-6> Ohm .cm at approximately -79 deg C and/or not more than 1 x 10<-6> Ohm .cm at approximately +20 deg C. Preferred Features: The material further contains Ca, Sr, Ba, Bi, Sb, Hg and Tl.
[ DE10007915 (PDF Format) ]
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http://www.rexresearch.com/djurek/djurek.htm
Apr 4, 2003
Can diamond now be a superconductor?
A physicist in South Africa claims to have created a new superconducting state of matter at room temperature. Johan Prins of the University of Pretoria observed the superconducting state in experiments with diamonds that had been doped with oxygen (Semiconductor Science and Technology 18 S131).
Diamond is a semiconductor and Prins has long been interested in using n-type diamond as a “cold” cathode to replace the “hot” cathodes found in television tubes and many other devices. Moreover, he believes that the results of his experiments on n-type diamond surfaces – made by exposing the diamond to energetic oxygen ions – can only be explained by a new type of superconducting state. “If it is not superconductivity then it must be violating the second law of thermodynamics,” he says.
In his experiments, Prins measures the current that flows between the diamond and a gold-plated probe as the distance between them is varied. When a voltage of +1000 V is applied, the current always settles down at a value of about 0.5 mA for separations up to about 16 µm, after which it falls to zero. A current also flows in the opposite direction when a voltage of –1000 V is applied, but it decreases more rapidly with distance. The experiments are performed at room temperature in a vacuum of 10–6 mbar.
Prins argues that a thin “electron-charge” layer is formed in the vacuum just above the surface of the diamond, and that a depletion layer of positive charges forms in the diamond. This is similar, he says, to the Schottky diode that is generated between an n-type semiconductor and a metal. Prins then applies the equations that describe electron transport through a Schottky diode to his system. He finds that as more and more electrons are extracted from the diamond, the density of electrons in this layer reaches a critical value at which a Bose–Einstein-type condensate of electron pairs forms. Current continues to flow from the diamond cathode through this layer to the anode, even though there is no voltage across the layer – a sign of superconductivity.
However, the rest of the diamond community remains to be convinced. Richard Jackman of University College London, who edited the special issue of the journal in which Prins’ papers appear, describes them as “largely theoretical papers, thought provoking and very controversial – the end conclusions remain open to debate”.
Prins admits that he must show that the state can expel magnetic fields to conclusively prove that the state is superconducting. However, he has recently retired and does not have the facilities to perform such an experiment. He has offered to fly his samples to another lab but has not yet found any volunteers. Prins and two colleagues are also trying to secure patents on the ideas.
In addition, Prins is half-way through writing six theoretical papers that will, he claims, fully explain the results and shed new light on the mechanisms underlying high-temperature superconductivity.
About the author
Peter Rodgers is Editor of Physics World
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http://physicsworld.com/cws/article/news/17244
10-2 Exploration of Room Temperature Superconductivity through the Super Strong-Coupling Superfluid Quantized Vortex
- A World of the Room Temperature Superconductivity Revealed by Quantized Vortices in Atomic Fermi Gas -
Fig.10-3
Fig.10-3
As seen in the central figure, vortices emerge everywhere inside an atomic gas when rotated using a laser (see the left-hand side figure). The vortices look like drilled holes in the atomic density profile. The vortex is quantized when the atomic gas enters the superfluid state. This study reveals structure of the quantized vortex by first principle calculation. Since the quantized vortex is a feature common to superfluidity and superconductivity, one can study the superconducting vortex through information for the superfluid vortex. Due to a strong attraction between atoms in the atomic gas, the vortex structure clarified by this study is considered to be equivalent to that of the superconducting vortex expected in the room temperature superconductivity.
It is said that "room temperature superconductivity may cause a revolution much beyond the Industrial Revolution".
Zero electrical resistance at the room temperature would allow transfer of energy created by an electric power plant without any loss, a global electrical energy transport, a high-speed transportation network by linear motor car, a laptop parallel supercomputer without any coolers and so on.
Due to such great possibilities, to raise the superconducting transition temperature up to the room temperature range is a dream of scientists today.
Very recently, study of the room temperature superconducting state is being attempted even though it has been not discovered yet.
This is because the superfluidity in the atomic Fermi gas realized on 2004, is a very strong coupling superfluidity whose impact would be equal to room temperature superconductivity. In general, the superconductivity emerges when two electrons form a pair via an attractive interaction. The strength of this attraction is known to determine the superconductivity transition temperature. The attractive interaction in the atomic Fermi gas is so strong that the attraction causes the superconductivity in a 1000K range much beyond the room temperature. This fact raises a question of what features the strong superfluid state has, and especially, what structure the vortex seen in the superfluid flow exhibits.
The vortex has a key role in both superfluid and superconductivity since its motion imposes a limitation on dissipation-free flow. Thus, one must inevitably study the vortex structure and its dynamics when considering the application of superconductivity.
In this study, we determined the vortex structure by a first-principle calculation, and succeeded in finding the structure from weak to strong attractive interaction beyond that of room temperature superconductivity.
As a consequence, it is found that the strong attraction leads to drastically lowered atom-density inside the vortex core like the depression in the middle of water inside a bucket when rotated, whereas in contrast there is little density depression in the weak attraction.
This result indicates that the electrical transport capacity of the room temperature [vortex] superconductor will be great. [better than a carbon nanotube poison]
We confirm through this study that the room temperature superconductivity may be quite fruitful if it is realized.
Top of this page
Reference
Machida, M. et al., Structure of a Quantized Vortex near the BCS-BEC Crossover in Atomic Fermi Gases, Physical Review Letters, vol.94, no.14, 2005, p.140401-1-140401-4.
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http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/mirai-en/2006/10_2.html
January 10, 2008
Is consciousness a by-product of room-temperature superconductivity?
Gbgiyuhuo_2
If so, it kind of makes us seem a bit less important in the greater scheme of things.
And generally — at least over the past 10,000 or so years — movement in that direction seems to be consistent with a more realistic view of things.
Yesterday, as I was reading Kenneth Chang's superb New York Times Science section story about the celebration last month of the fiftieth anniversary of the publication of "Theory of Superconductivity," a landmark paper which appeared in Physical Review in December 1957, I got to reflecting on the halting progress of high-temperature superconductivity studies in the decades since.
And then I got to thinking about how it is that after all these years and myriad conflicting theories, we seem no closer to a theory of consciousness today than we were fifty years ago.
Well, the way I see it, if you're getting nowhere in two different avenues, that's no reason not to see what happens when you combine them.
Wasn't it the noted physicist Billy Preston who wrote, "Nothin' from nothin' leaves nothin'?"
Addition by subtraction — that's where it's at.
Here's the Times article.
When Superconductivity Became Clear (to Some)
Superconductivity, the flow of electricity without resistance, was once as confounding to physicists as it is to everyone else.
For almost 50 years, the heavyweights of physics brooded over the puzzle. Then, 50 years ago last month, the answer appeared in the journal Physical Review. It was titled, simply, “Theory of Superconductivity.”
“It’s certainly one of the greatest achievements in physics in the second half of the 20th century,” said Malcolm R. Beasley, a professor of applied physics at Stanford.
Superconductivity was discovered in 1911 by a Dutch physicist, Heike Kamerlingh Onnes.
He observed that when mercury was cooled to below minus-452 degrees Fahrenheit, about 7 degrees above absolute zero, electrical resistance suddenly disappeared, and mercury was a superconductor.
For physicists, that was astounding, almost like happening upon a real-world perpetual motion machine. Indeed, an electrical current running around a ring of mercury at 7 degrees above absolute zero would, in principle, run forever.
If the phenomenon defied intuition, it also defied explanation.
After wrapping up special and general relativity [which was unsatisfactory to him], Albert Einstein tried, and failed, to devise a theory of superconductivity. Werner Heisenberg, the physicist who came up with the Heisenberg uncertainty principle, struggled with the problem, as did other pioneers of quantum mechanics like Niels Bohr and Wolfgang Pauli.
Felix Bloch, another thwarted theorist, jokingly concluded: Every theory of superconductivity can be disproved.
This long list of failure was unknown to Leon N. Cooper. In 1955 he had just received his Ph.D. and was working in a different area of theoretical physics at the Institute for Advanced Study in Princeton when he met John Bardeen, a physicist who had already won fame for the invention of the transistor.
Bardeen, who had left his transistor research at Bell Labs for the University of Illinois, wanted to recruit Dr. Cooper for his latest grand research endeavor: solving superconductivity.
“I talked to John for a while,” Dr. Cooper recalled at a conference in October, “and he said, ‘You know, it’s a very interesting problem.’ I said, ‘I don’t know much about it.’ He said, ‘I’ll teach you.’
“He omitted to mention,” Dr. Cooper said, “that practically every famous physicist of the 20th century had worked on the problem and failed.”
Bardeen himself had already made two unsuccessful assaults. Dr. Cooper said the omission was fortunate, because “I might have hesitated.”
Dr. Cooper arrived at the University of Illinois in September 1955. In less than two years, he, Bardeen and J. Robert Schrieffer, a graduate student, solved the intractable puzzle.
Their answer is now known as B.C.S. theory after the initials of their last names.
Bardeen died in 1991, but Dr. Cooper and Dr. Schrieffer returned to the University of Illinois in October to commemorate the publication of their superconductivity paper.
Their Herculean achievement was honored with the 1972 Nobel Prize in physics, and it deeply influenced theorists who were putting together theories explaining the to and fro of fundamental particles.
The theory has also been applied in subjects as far flung as the dynamics of neutron stars.
B.C.S. theory, however, never achieved recognition in popular culture like relativity and quantum mechanics. That may be understandable given the theory’s complexities, applying quantum mechanics to the collective behavior of millions and millions of electrons. “They were very, very difficult calculations,” Dr. Cooper recalled. “They were superdifficult.”
Even for physicists, the 1957 paper was a difficult one to read.
On the first day of the October conference, Vinay Ambegaokar of Cornell held up a small notebook from 1958. The notebook, Dr. Ambegaokar said, “shows I read it, but I did not understand it.” He said that he continued to prefer approaches “with less constant intellectual effort.” (Soviet physicists had come up with a so-called phenomenological theory — equations that described the behavior of superconductors but did not explain what created that behavior.)
Electrical resistance arises because the electrons that carry current bounce off the nuclei of the atoms, like balls in a diminutive pinball machine. The nuclei recoil and vibrate, sapping energy from the electrons.
In a superconductor, electrons seem more like ghosts than particles, passing the nuclei as if they were not there.
Clues to the nature of superconductivity began to accumulate when Walther Meissner and Robert Ochsenfeld, two German physicists, measured the magnetic field inside a superconductor and discovered, to everyone’s surprise, that it was exactly, precisely zero.
Further, any magnetic field that was present in a material would disappear as it was cooled into a superconductor.
This phenomenon, known as the Meissner Effect, was the first sign that superconductors were more than just the perfect conductors envisioned in the early theories.
Then there were signs of a large energy gap between the lowest energy, superconducting state and the next possible, higher-energy configuration. That kept the electrons trapped in the superconducting state.
Finally, experiments showed that the temperature at which an electrical resistance disappeared varied when heavier or lighter versions of an atom were substituted; the weight of atoms play a negligible role in the electrical resistance of ordinary conductors.
Bardeen believed that if he could understand the energy gap, he would understand superconductivity.
In 1955, David Pines — Dr. Schrieffer’s predecessor in the Bardeen group — came up with the first breakthrough.
Negatively charged electrons generally repulse each other, but Dr. Pines showed that vibrations in the lattice of nuclei could generate a minuscule attraction.
When an electron passes near a positively charged atomic nucleus, the opposite electric charge slightly pulls the nucleus toward the electron. The electron flits away, leaving behind a positively charged wake, and that, in turn, attracts other electrons.
Dr. Pines’s result showed why the weight of the atoms mattered — heavier atoms accelerate more slowly.
The next two key breakthroughs came via mass transit.
In December 1956, Dr. Cooper was on a 17-hour train ride to New York City. He had spent his first months applying his theoretical bag of tricks on the equations. “I did it and I did it and I did it, and I got absolutely nowhere,” he said. “I wasn’t feeling that clever any more.”
On the train, Dr. Cooper discarded his failed calculations. “I just thought and thought, ‘I know this is a difficult problem, but it seems so simple,’” he said. Physicists think of electrons in a normal conductor as piling on top of one another in a “Fermi sea,” named after Enrico Fermi, who was still formulating the theory at the University of Chicago.
Dr. Cooper realized that it was only the electrons near the top of the Fermi sea that were crucial.
“You introduce a small effect,” he said, “and somehow you get a superconductor.”
As he worked on the problem for the next few months, Dr. Cooper realized that these electrons not only attracted others as Dr. Pines had shown, but also grouped themselves into pairs.
It now seemed that superconductivity depended on these pairs, subsequently named Cooper pairs.
Contrary to simple expectations, the two electrons did not revolve closely around each other but were far apart, with many other electrons in between. The multitude of overlapping pairs made the calculations a morass.
A year after Dr. Cooper’s trip, Dr. Schrieffer headed to New York for a scientific conference.
(At the same time, Bardeen headed to Stockholm to collect his first Nobel Prize, for the transistor.)
Dr. Schrieffer had been looking at statistical approaches to solve the tangle of Cooper pairs. On the subway, he wrote down the answer, which turned out to be fairly simple in form.
The Cooper pairs essentially coalesced into one large clump that moved together, and the energy gap prevented the scattering of any one pair. Dr. Schrieffer gives the analogy of a line of ice skaters, arm in arm. “If one skater hits a bump,” he said, the skater is “supported by all the other skaters moving along with it.”
Back in Illinois, he showed what he had written to Dr. Cooper and then Bardeen. Bardeen was convinced.
Charles P. Slichter, a professor of physics at Illinois then and now and who had conducted many of the experiments teasing out the clues to superconductivity, remembered Bardeen’s stopping him in the hallway one day.
“John wasn’t a great talker,” Dr. Slichter said. “I could see he had something he wanted to say, and we sort of stood there. It seemed like we stood there for five minutes.”
Dr. Slichter was tempted to say something, “but I knew I shouldn’t, because if I did, I would shut him up. So he spoke to me finally. ‘Well, Charlie, I think we’ve solved superconductivity.’
“And wow, it is the most exciting moment in science I’ve ever experienced,” Dr. Slichter said.
In February 1957, the three submitted a paper, essentially outlining their ideas, to Physical Review. Their longer, more complete paper did not appear in print until December that year.
A new puzzle appeared in 1986 with the discovery of so-called high-temperature superconductors.
These superconductors work at higher, though still very low, temperatures.
No theory has emerged as convincing; one session at the Illinois conference was a mass interrogation of the competing theorists.
The theorists agreed that high-temperature superconductors were different, that the attractive force did not come from the vibrations of nuclei. Rather, they said, the attraction somehow arose from the flipping of the atoms’ tiny magnetic poles. Beyond that, they did not agree.
Other types of superconductors, and more theories, could well follow.
As Dr. Beasley of Stanford said in the closing talk of the conference: “We have no idea of the limits of superconductivity in the universe. If 85 percent of the universe is dark matter, I hope 5 percent of it is superconducting.”
....................
What triggered my thought connecting superconductivity to consciousness was the final sentence of the legend of the figure up top (by Jonathan Corum, it accompanied the Times article), to wit, "With no resistance, the current may persist for years."
Huh.
Let's see... what else is measured in years?
Hey, I know: a human life.
Instead of calorie restriction and the like, maybe longevity researchers should instead focus on promoting the conditions which allow the "miracle" (in quotes because both miracles and magic usually turn out to result from superior technology... but I digress) of consciousness to flourish for decades at body temperature before choosing another venue.
Here's a link to "... 4,652 free online papers on consciousness...."
That ought to keep you occupied for the rest of the day.
Knock yourself out.
January 10, 2008 at 10:01 AM | Permalink
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Comments
PBS Nova had an excellent show this week on the History of Cold, and discussed superconductivity. Fairly interesting.
Posted by: Elux Troxl | Jan 10, 2008 11:56:00 AM
No one "invented" the transistor any more than anyone invented air. The characteristic operation of a three-part semiconductor combination was DISCOVERED by the great William Shockley in the 1950s. Even Shockley initially could work out how it worked. I've never heard of the guy you mention in your article.
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http://www.bookofjoe.com/2008/01/is-consciousnes.html
Given ORME gold and 'starfire' and consciousness, the previous author I think is onto something about superconductivity and consciousness, at least ORME enhanced versions. ORME loses mass/inertia as well, and appears as different elements, another strange "DePalma" effect.
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