Innovative superconductor fibers carry 40 times more electricity

Innovative superconductor fibers carry 40 times more electricity

  12:49:00 AM    Science Lover

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Wiring systems powered by highly-efficient superconductors have long been a dream of science, but researchers have faced such practical challenges such as finding pliable and cost-effective materials. Now researchers at Tel Aviv University have found a way to make an old idea new with the next generation of superconductors.

This is a demonstration of "quantum trapping"
in Dr. Almog's laboratory. Credit: AFTAU

Dr. Boaz Almog and Mishael Azoulay working in the group of Prof. Guy Deutscher at TAU's Raymond and Beverly Sackler School of Physics and Astronomy have developed superconducting wires using fibers made of single crystals of sapphire to be used in high powered cables. Factoring in temperature requirements, each tiny wire can carry approximately 40 times more electricity than a copper wire of the same size. They have the potential to revolutionize energy transfer, says Dr. Almog.

High power superconductor cables take up much less space and conduct energy more efficiently, making them ideal for deployment across grids of electricity throughout a city. They will also offer a more effective method for collecting energy from renewable sources, such as solar and wind energy. Superconducting wires can also be used for energy storage and enable devices which enhance grid stability.

The new superconductors were first presented at the Israel Vacuum Society Conference in June 2011, and will be shown at both the European Conference on Applied Superconductivity and the Association of Science Technology Centers Conference this fall.

Beating the heat

One of the things that make our copper wires inefficient is overheating, Dr. Almog explains. Due to electrical resistance found in the metal, some of the energy that flows through the cables is cast off and wasted, causing the wires to heat up. But with superconductors, there is no resistance. A self-contained cooling system, which requires a constant flow of liquid nitrogen, keeps the wire in its superconducting state. Readily available, non-toxic, and inexpensive — a gallon of the substance costs less than a gallon of milk — liquid nitrogen provides the perfect coolant.

Even with the benefit of liquid nitrogen, researchers were still hard pressed to find a material that would make the ideal superconductor. Superconductors coated on crystal wafers are effective but too brittle, says Dr. Almog, and although superconductors on metallic tapes had some success, the product is too expensive to manufacture in mass quantities.



To create their superconductors, the researchers turned to sapphire fibers, developed by Dr. Amit Goyal at the Oakridge National Lab in Tennessee and lent to the TAU team. Coated with a ceramic mixture using a special technique, these single-crystal fibers, slightly thicker than a human hair, have made innovative superconductors.

Going macro

Dr. Almog is currently working to produce better superconductors that could transport even larger amounts of electric current.

One area where such superconductors could lend a hand is in collecting renewable energy sources. "Sources such as wind turbines or solar panels are usually located in remote places such as deserts or offshore lines, and you need an efficient way to deliver the current," explains Dr. Almog. These superconductors can traverse the long distances without losing any of the energy to heat due to electrical resistance.

Superconducting cables could also be an efficient way to bring large amounts of power to big cities "If you want to supply current for a section of a city like New York, you will need electric cables with a total cross-section of more than one meter by one meter. Superconductors have larger current capacities using a fraction of the space," says Dr. Almog. Different parts of a city could be cross-wired, he adds, so that in the event of a blackout, power can be easily rerouted.

Inspiring young scientists

Developing a superior superconductor is only part of TAU's mission. Dr. Almog is also dedicated to making this technology accessible and exciting as a way to capture the imagination of aspiring scientists. TAU has manufactured superconductor wafers which, filled with liquid nitrogen like their cable cousins, can be locked in place by strong magnets and levitate. Placed on a magnetic track, the wafer zooms through the air like George Jetson's space-age car. It might look like magic, but it's actually a phenomenon called "quantum trapping." Kits that demonstrate this "magnetic levitation" have been distributed in science museums throughout Israel, and Dr. Almog hopes to expand their distribution internationally.

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Etch-a-sketch with superconductors

Etch-a-sketch with superconductors

  10:26:00 AM    Science Lover

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Reporting in Nature Materials this week, researchers from the London Centre for Nanotechnology and the Physics Department of Sapienza University of Rome have discovered a technique to 'draw' superconducting shapes using an X-ray beam. This ability to create and control tiny superconducting structures has implications for a completely new generation of electronic devices.

In future, X-ray beams could be used to write superconducting circuits, such as those depicted in the image. Here, solid lines indicate electrical connections while semicircles denote superconducting junctions, whose states are indicated by red arrows. Credit: UCL Press Office

Superconductivity is a special state where a material conducts electricity with no resistance, meaning absolutely zero energy is wasted.

The research group has shown that they can manipulate regions of high temperature superconductivity, in a particular material which combines oxygen, copper and a heavier, 'rare earth' element called lanthanum. Illuminating with X-rays causes a small scale re-arrangement of the oxygen atoms in the material, resulting in high temperature superconductivity, of the type originally discovered for such materials 25 years ago by IBM scientists. The X-ray beam is then used like a pen to draw shapes in two dimensions.

A well as being able to write superconductors with dimensions much smaller than the width of a human hair, the group is able to erase those structures by applying heat treatments. They now have the tools to write and erase with high precision, using just a few simple steps and without the chemicals ordinarily used in device fabrication. This ability to re-arrange the underlying structure of a material has wider applications to similar compounds containing metal atoms and oxygen, ranging from fuel cells to catalysts.



Prof. Aeppli, Director of the London Centre for Nanotechnology and the UCL investigator on the project, said: "Our validation of a one-step, chemical-free technique to generate superconductors opens up exciting new possibilities for electronic devices, particularly in re-writing superconducting logic circuits. Of profound importance is the key to solving the notorious 'travelling salesman problem', which underlies many of the world's great computational challenges. We want to create computers on demand to solve this problem, with applications from genetics to logistics. A discovery like this means a paradigm shift in computing technology is one step closer."

Prof Bianconi, the leader of the team from Sapienza, added: "It is amazing that in a few simple steps, we can now add superconducting 'intelligence' directly to a material consisting mainly of the common elements copper and oxygen."

More information: The X-ray experiments were performed at the Elettra (Trieste) synchrotron radiation facility. The work is published in Nature Materials, 21 August 2011 (doi:1038/nmat3088) and follows on from previous discovery of fractal-like structures in superconductors (doi:10.1038/nature09260).

Provided by University College London

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Ultrafast switch for superconductors

Ultrafast switch for superconductors

  1:12:00 AM    Science Lover

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A high-temperature superconductor can now be switched on and off within a trillionth of a second – 100 years after the discovery of superconductivity and 25 years after the first high-temperature superconductor was. A team including physicists from the University of Oxford and the Max Planck Research Group for Structural Dynamics at the University of Hamburg has realised an ultrafast superconducting switch by using intense terahertz pulses. This experiment opens up the possibility to discover more about the still unsettled cause of this type of superconductivity, and also hints at possible applications for ultrafast electronics in the future.

The superconducting transport between the layers of a cuprate crystal (three layers, red and blue spheres represent the oxygen and copper atoms respectively) is controlled with an ultrashort terahertz pulse (yellow in the background). The three-dimensional superconductivity can thus be switched on and off very quickly (orange spheres represent electrons). © J.M. Harms, Max Planck Research Group for Structural Dynamics

Superconductivity is one of the most remarkable effects in physics. Every electrical conductor has a resistivity, but some materials lose their resistivity completely if they are cooled to below a characteristic temperature; the current then flows without any loss whatsoever. When the Dutch physicist Heike Kamerlingh Onnes discovered this effect in 1911 in mercury, he initially believed that his measuring instruments were faulty, before he became aware of the significance of his monumental discovery.

“Normal” conductors such as mercury or lead must be cooled down to temperatures near absolute zero at minus 273.16 degrees Celsius in order to become superconducting. It was therefore a sensation when, in 1986, Johannes Georg Bednorz and Karl Alexander Müller presented a ceramic material that already became superconducting at minus 248 degrees Celsius. Since then, these cold conductors have been a burning issue with both scientists working in basic research and users. The ultrafast switch, which has now been developed by the research group working with Andrea Cavalleri, head of the Max Planck Research Group for Structural Dynamics at the University of Hamburg, is a further astonishing discovery in this field.

The high-temperature superconductor used by the Hamburg scientists has been known for a long time. It is a crystal based on lanthanum cuprate (La2CuO4) to which a specific quantity of strontium has been added (La1,84Sr0,16CuO4). Its transition temperature is minus 233 degrees Celsius. Although it is not yet completely clear how the superconductivity arises here, essential elements are known: “The crystal is formed by copper-oxygen planes which lie on top of each other like the pages of a book,” explains Cavalleri. The electrons can only move within these planes; the current transport therefore only occurs in two dimensions.

If the material is cooled below 40 Kelvin, a link is suddenly created between these two planes. Physicists explain this using the wave model, according to which the electrons are pictured not as particles, but as waves. Below the transition temperature the electrons from neighbouring planes overlap, and this allows the electric charge carriers to change from one plane to the other. Current is suddenly transported in all three spatial dimensions: the superconducting state has been created.

A terahertz pulse briefly destroys the coupling of the electrons
Cavalleri and his colleagues then wanted to know whether this transport between the layers can be deliberately interrupted and switched on again. In theory this is possible if a very strong electric field is applied at right angles to the layers. However, applying such a field is impractical. “This causes the crystal to heat upand the superconductivity collapses,” explains Cavalleri. The solution was to send in an ultrashort pulse of light to manipulate the superconductor.



This so-called terahertz pulse is an electromagnetic wave, similar to light, but with a much longer wavelength. It has an electric field that briefly destroys the coupling of the electron waves between the planes when it penetrates into the crystal. This is only successful if the electric field strength of the pulse is very high, in the order of several ten thousand volts per centimetre. And it must be short enough that it does not heat up the crystal.

Only recently has it been possible to generate such extremely powerful, ultrashort terahertz pulses. This is the task of team member Matthias Hoffmann. In very simple terms, this is done by the interaction of an ultrashort laser pulse with a lithium niobate crystal. An effect which physicists call optical rectification then generates the desired terahertz radiation in the crystal.

The experiment, which Andreas Dienst designed and carried out in Oxford, succeeded as anticipated: for the short time of less than one picosecond (10-12 seconds) as the pulse interacts with the superconductor, the coupling between the planes, and thus the superconductivity, was interrupted before subsequently returning. The superconductor does not suffer in this process and can be switched as often as one likes.

“This is a very fascinating result, because we can also use this method to investigate how high-temperature superconductors work,” says Cavalleri. It is also possible that this effect additionally has real-world applications. Basically, the switchable high-temperature superconductor works in a very similar way to a conventional field-effect transistor. This is a semiconductor whose ability to pass a current can be controlled by applying an electric voltage. Analogous to this, is conceivable that the high-temperature superconductor could be used as an ultrafast, nanoelectronic transistor that is controlled by microwaves.

More information: A. Dienst, M. Hoffmann, D. Fausti, J. Petersen, S. Pyon, T. Takayama, H. Takagi, A. Cavalleri, Bi-directional ultrafast electric-field gating of interlayer charge transport in a cuprate superconductor, Nature Photonics, adv. Online public., 26. Juni 2011, DOI: 10.1038/NPHOTON.2011.124

Provided by Max-Planck-Gesellschaft

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Einstein's theory applied to superconducting circuits

Einstein's theory applied to superconducting circuits

  6:14:00 PM    Science Lover

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In recent years, UC Santa Barbara scientists showed that they could reproduce a basic superconductor using Einstein's general theory of relativity. Now, using the same theory, they have demonstrated that the Josephson junction could be reproduced. The results are explained in a recent issue of the journal Physical Review Letters.

The gravitational description of the superconducting 
condensate shows a suppression in the gap. 
(Credit: Jorge Santos, UCSB)

The Josephson junction, a device that was first discovered by Brian David Josephson in the early 1960s, is a main ingredient in applications of superconductivity.

Gary Horowitz, professor of physics at UC Santa Barbara, said that Einstein's general theory of relativity — which was developed as a theory of gravity and is extremely successful in explaining a wide variety of gravitational phenomena — now is being used to explain several aspects of non-gravitational physics.

"The basic phenomenon with Josephson junctions is that you can take two superconductors, separate them by a little gap, and still find current going across it, in a specific way," said Horowitz. "And that has found many applications. So the Josephson junction is something we've reproduced using general relativity."

Horowitz said that he and his co-authors used tools from string theory to develop the gravity model of a superconductor. He explained that it was surprising to be able to link Einstein's general theory of relativity to a totally different area of physics. He said he hoped that the new tools would one day be able to shed light on new types of superconductors.

"Most materials, if you cool them down sufficiently, will actually conduct electricity without any resistance," said Horowitz. "These are superconductors. There is a standard theory of superconductivity, discovered about 50 years ago, that has worked well for most of the so-called conventional superconductors."

A new class of materials was discovered 25 years ago. These are superconductors that have zero resistance at somewhat higher temperatures. Physicists are still working on understanding the mechanism.

This new class of materials involves copper-oxygen planes. Another new class of superconductors, based on iron instead of copper, was discovered a couple of years ago. These materials, called iron nictides, also have the property of superconducting at a higher temperature.

"There is a lot of activity and interest in understanding these materials," said Horowitz. "Ultimately, the goal is to have a room-temperature superconductor, which, you can imagine, would have lots of interesting applications."

Horowitz and his research team found what could be called a gravitational model, or a gravitational dual — a dual description of a superconductor using gravity, black holes, and all of the traditional ingredients of general relativity. "This came as quite a surprise because this is a totally different area of physics, which is now being connected to this condensed matter area," said Horowitz.

Provided by UC Santa Barbara

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Roller Coaster Superconductivity Discovered

Roller Coaster Superconductivity Discovered

  10:17:00 AM    Science Lover

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Superconductors are more than 150 times more efficient at carrying electricity than copper wires. However, to attain the superconducting state, these materials have to be cooled below an extremely low, so-called transition temperature, at which point normal electrical resistance disappears. Developing superconductors with higher transition temperatures is one of physics' greatest quests.

This graphic shows the crystal structure of three-
layered bismuth oxide. (Credit: Xiao-Jia Chen)

Now, researchers at the Carnegie Institution's Geophysical Laboratory, with colleagues, have unexpectedly found that the transition temperature can be induced under two different intense pressures in a three-layered bismuth oxide crystal referred to as "Bi2223." The higher pressure produces the higher transition temperature. They believe this unusual two-step phenomena comes from competition of electronic behavior in different kinds of copper-oxygen layers in the crystal.

The work is published in the August 19, 2010, issue of Nature.

Until now, copper-laden materials called cuprates have been the only superconductors whose transition temperatures are higher than the liquid nitrogen boiling point at -321°F (77 K). Whether researchers can make transition temperatures higher in such materials remains a challenge.

"Bi2223 is like a layered cake," explained lead author Xiao-Jia Chen at Carnegie. "On the top and bottom there are insulating bismuth-oxide layers. On the inside of those, come layers of strontium oxide. Next, are layers of copper oxide, then calcium, and finally the middle is another copper-oxide layer. Interestingly, the outermost and inner layers of copper oxide have different physical properties resulting in an imbalance of electric charge between the layers."

One way scientists have found to increase the transition temperature of superconducting materials is to "dope" them by adding charged particles.

Under normal pressure, the optimally doped Bi2223's transition temperature is -265°F (108K). The scientists subjected doped crystals of the material to a range of pressures up to 359,000 times the atmospheric pressure at sea level (36.4 Giga Pascal), the highest pressure yet for magnetic measurements in cuprate superconductors. The first higher transition temperature happened at 100,666 atmospheres (10.2 GPa).

"After that, increasing pressures ended up with lower transition temperatures," remarked Chen. "Then to our complete surprise at about 237,000 atmospheres (24 GPa) the superconducting state reappeared. Under even more pressure, 359,000 atmospheres, the transition temperature rose to -215°F (136K). That was the highest pressure our measuring system could detect."

Other research has shown that some multilayered superconducting materials like this one exhibit different electronic and vibrational behaviors in different layers. The researchers think that 237,000 atmospheres might be a critical point where pressure suppresses one behavior and enhances superconductivity.

"The finding gives new perspectives on making higher transition temperature in multilayer cuprate superconductors. The research may offer a promising way of designing and engineering superconductors with much higher transition temperatures at ambient conditions," concluded coauthor Viktor Struzhkin also of Carnegie.

The research was supported by the U. S. Department of Energy, Carnegie Canada, and the National Natural Science Foundation of China.

This work was conducted in collaboration with researchers at the South China University of Technology and Max Plank Institute for Solid State Research in Germany.

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Superconducting Hydrogen

Superconducting Hydrogen

  7:02:00 PM    Science Lover

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Physicists have long wondered whether hydrogen, the most abundant element in the universe, could be transformed into a metal and possibly even a superconductor -- the elusive state in which electrons can flow without resistance.

Periodic table detail of hydrogen. (Credit: iStockphoto/David Freund)

 

They have speculated that under certain pressure and temperature conditions hydrogen could be squeezed into a metal and possibly even a superconductor, but proving it experimentally has been difficult. High-pressure researchers, including Carnegie's Ho-kwang (Dave) Mao, have now modeled three hydrogen-dense metal alloys and found there are pressure and temperature trends associated with the superconducting state -- a huge boost in the understanding of how this abundant material could be harnessed.

The study is published in the January 25, 2010, early, on-line edition of the Proceedings of the National Academy of Sciences.

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