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Topic: High temperature superconductivity

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		The general view point (determined by "majority vote") seems to be that low temperature superconductors are phonon mediated whereas high Tc ones are somehow "unconventional" and anisotropic, although the origin of the anisotropy remains controversial.
		Discovered in 1987, high temperature superconductivity in the copper oxide ceramics continues to be the most nettling problems in modern solid state physics.
		The complexity and difficulties with high temperature superconductivity is well illustrated by the Buddhist parable of the blind men trying to describe “experimentally” an elephant.
	www.lycos.com /info/superconductivity--high-temperature-superconductivity.html (755 words)

	UCR: French-German Group Verifies High-Temperature Superconductivity Theory Proposed by UCR Physicist
		The verification ultimately could assist in the fabrication of materials that are superconducting at room temperature and help settle a contentious, international debate on the fundamental physics of superconductivity and emergent states of matter.
		Varma’s initial theory, which he proposed in 1989 when he was at Bell Laboratories, stated the radical idea that high temperature superconductivity and related phenomena occur in certain materials because quantum-mechanical fluctuations in these materials increase as temperature decreases.
		In these experiments a beam of neutrons changes direction as well as the direction of its magnetization in a manner that is closely related to the geometrical arrangement of the current loops inside the material in which the beam is made to pass.
	www.newsroom.ucr.edu /cgi-bin/display.cgi?id=1337 (850 words)

	Science News: High-temperature superconductivity: what's here... @ HighBeam Research (Site not responding. Last check: 2007-11-05)
		But to be successful, says Chu, the superconducting interconnects must overcome contact problems with other parts of the system that could generate heat buildup and possibly squelch the superconductivity effects.
		Since the superconducting properties can change over a length of 15 or 20 angstroms, says Rowell, the last 15 angstroms near the surface of the sample in a tunnel junction must have the necessary oxygen content and full superconducting properties in order to work.
		At current liquid-nitrogen temperatures, the volume of the magnet that would store the car's energy would be almost the size of the car, and the weight of the superconducting wire would be 2,000 pounds.
	www.highbeam.com /library/doc0.asp?DOCID=1G1:5160848&refid=ip_encyclopedia_hf (2181 words)

	Very Short High-Efficiency Superconducting Antennas for Long Wave Communications (Site not responding. Last check: 2007-11-05)
		In February 1987, a still higher superconducting record of 92 K was made by scientists at the University of Houston and the University of Alabama in Huntsville who substituted yttrium for lanthanum bringing superconductivity into the liquid nitrogen range.
		= loading coil resistance (~0 in superconducting coils assuming the superconducting ac-losses are negligible), and h = distance between the loading coil and the feed point in fractions of wavelength expressed in degrees.
		The first microwave superconducting antenna is credited to the Electronic Materials and Devices Research Group at the University of Birmingham (United Kingdom) and this group was recently presented with the International IEE Premium Award for their work.
	ecjones.org /hightc.html (2686 words)

	High-Temperature Superconductivity (Site not responding. Last check: 2007-11-05)
		One of the most exciting challenges of modern solid state physics is to unravel the underlying microscopic mechanism of high-temperature superconductors.
		We are presently working on a microscopic theory of high-temperature superconductivity that incorporates the findings of angle-resolved photo-emission spectroscopy in the cuprates.
		These highly nonlinear devices are the backbone of superconducting electronics and possess a large number of degrees of freedom that lead to chaotic behaviour.
	www.phy.hw.ac.uk /resrev/hts~1.htm (284 words)

	Neutrons Provide Clues To High Temperature Superconductivity
		Superconductivity was discovered in 1911 and occurs in many ordinary metals such as lead and aluminum at very low temperatures (below about 5 degrees above absolute zero, or about 290 degrees below room temperature).
		In these "high temperature" superconductors, the chemical elements copper and oxygen are arranged in a layered structure, with other elements sandwiched between the layers.
		It is to be hoped that a comprehensive theory of high temperature superconductivity will lead to the design of materials which superconduct at even higher temperatures, perhaps eventually room temperature.
	www.sciencedaily.com /releases/1999/04/990415065141.htm (851 words)

	Physics Underlying High-Temperature Superconductivity
		This is consistent with theoretical models which hold that high-Tc superconductivity involves fluctuations of the magnetic spins of atomic nuclei rather than the phonon-mediated mechanism (vibrations in the atomic lattice) of classical low-Tc superconductors.
		Operable at temperatures as low as 0.25 degrees above absolute zero and capable of simultaneously measuring both the surface topography and the density of state of a sample with atomic resolution, this STM is optimized for the study of high-Tc superconducting materials.
		Made from niobium and operable in a powerful magnetic field (7.2 Tesla), this superconducting tip could give Davis and his colleagues the ability to study the magnetic spins of individual atoms which would be a major advance towards unlocking the secrets of high-Tc superconductivity.
	enews.lbl.gov /Science-Articles/Archive/super-mechanism.html (1141 words)

	Big step to high-temperature superconductors
		Rapid progress with ultracold superfluid gases in the lab over the past year has physicists confident that a full explanation of high-critical-temperature superconductivity is just around the corner.
		The fermions can enter a superfluid state at low temperatures by pairing up so that the spin of each pair becomes an integer; when that happens, the pairs represent bosonic particles and are able to share the same quantum state and flow without resistance.
		As the coupling becomes tighter, the corresponding "temperature" of the group of electrons modeled by the gas increases.
	www.eetasia.com /ART_8800374235_480100_0b0ab8d1.HTM (1016 words)

	McMaster physicist heats up physics debate (Site not responding. Last check: 2007-11-05)
		Low-temperature superconductivity is used in MRI machines, but Timusk said the technology that cools the coils to reach low temperatures is costly, necessitating the MRI’s small and tunnel-like shape.
		Timusk used a different measurement tool known as “infra-red optics” to study the same material, and he discovered that the “kink” that appears in high-temperature superconductivity can be eliminated when oxygen is added without destroying the high temperature superconductivity.
		That means the infra-red instrument provides a clearer output of what’s happening to the energy of the superconducting electrons and rules out any significant role of the phonons in high temperature superconductivity.
	www.mcmaster.ca /ua/opr/nms/newsreleases/2004/timusk.html (549 words)

	Study gives lowdown on high-temperature superconductivity
		Superconductivity is a phenomenon that occurs when certain metals are cooled to near absolute zero, a temperature equivalent to zero degrees Kelvin (K), -273 C or -459 F. In ceramic materials, the phenomenon appears at about 100K.
		Previous studies on superconductors have established that while the critical temperature rises as the number of layers increase from one to three, it then drops off.
		Scientists have previously suggested that the critical temperature increase between one- and three-layered materials is due to the ability of electron pairs to tunnel between the layers of superconducting material.
	www.eurekalert.org /pub_releases/2004-03/uot-sgl030304.php (514 words)

	Can phonons help explain high-temperature superconductivity? (August 2001) - News - PhysicsWeb (Site not responding. Last check: 2007-11-05)
		Superconductivity - the absence of electrical resistance in a material - is observed when the material is cooled below the superconducting transition temperature.
		By the mid-1980s the highest known transition temperature was 23 Kelvin.
		In 1986, however, materials that became superconducting at much higher temperatures were discovered, and the record transition temperature is now around 130 Kelvin.
	physicsweb.org /articles/news/5/8/2 (421 words)

	Physics News Update Number 173 - IS HIGH-TEMPERATURE SUPERCONDUCTIVITY d-WAVE (Site not responding. Last check: 2007-11-05)
		Low-temperature superconductivity is characterized by "s-wave" Cooper pairs.
		By contrast, in high- temperature superconductivity, some theorists believe, the Cooper pairs are in "d-wave" states having an angular momentum of two units.
		This half-integral flux had never been directly observed before, and the IBM scientists believe that their finding supports, but does not yet prove, the notion that the electron pairing in their high-temperature superconductor is d-wave in nature.
	www.aip.org /pnu/1994/split/pnu173-2.htm (199 words)

	PHASE TRANSITION APPROACH TO HIGH TEMPERATURE SUPERCONDUCTIVITY (Site not responding. Last check: 2007-11-05)
		The discovery of superconductivity at 30 K by Bednorz and Müller in 1986 ignited an explosion of interest in high temperature superconductivity.
		A great deal of experimental data is now available on the cuprates, and various properties have been well characterized using high quality single crystals and thin films.
		Despite this enormous research effort, however, the underlying mechanisms responsible for superconductivity in the cuprates are still open to question.
	www.worldscibooks.com /physics/p206.htm (220 words)

	An Introduction to High Temperature Superconductivity (Site not responding. Last check: 2007-11-05)
		By the end of 1986, superconductivity research achieved revolutionary advances with the effort of Paul C. Chu and colleagues at the University of Houston.
		Signs of superconductivity above 77 K were repeatedly observed in poorly-characterized samples during the period, strongly affirming the belief in the existence of superconductivity in the liquid-nitrogen temperature range.
		Bismuth and thallium superconducting systems were discovered in 1988 which superconduct at 110 K and 125 K, respectively.
	www.physnet.uni-hamburg.de /home/vms/reimer/htc/htc.html (640 words)

	High-Temperature Superconductivity In Japan
		Because of its perceived scientific and technological importance, superconductivity had been selected as a flagship to show the world that the Japanese could be successful in fundamental scientific research.
		Most of the outstanding achievements of the Japanese in the field of superconductivity stemmed from this systematic approach, which was reinforced by a top-down management structure and an appreciation of the people who did materials synthesis, processing, and scale-up.
		The equipment and facilities for superconductivity RandD in Japanese industry and national laboratories were equal or superior to those in the United States and were steadily improving.
	www.wtec.org /loyola/ar93_94/hts.htm (966 words)

	Science News: High-powered discussions on high-temperature superconductivity
		In the BCS theory, that mediator is a phonon, which causes the electrons to attract through vibrations in the crystal lattice structure of the superconducting material.
		Although room-temperature superconductivity is still expected to be achieved someday, most groups are concentrating their efforts on the materials that superconduct in the 95 K range.
		Several researchers note the importance of looking for new examples of materials that superconduct, or of peering into the reasons why some of the rare earths apparently don't superconduct.
	www.findarticles.com /p/articles/mi_m1200/is_n23_v132/ai_6213753 (947 words)

	Researchers Peg Magnetism as Key Driver of High-Temperature Superconductivity
		Researchers found that in materials that superconduct at high temperatures, magnetic excitations (large peak) play a key role in pairing the electrons.
		An important missing piece in the puzzle of high-temperature superconductivity, the finding should boost efforts to develop a variety of useful technologies now considered impractical for conventional superconductors, which work at markedly lower temperatures.
		Better understanding of the mechanism of high-temperature superconductivity may lead to the discovery of new materials in which electrical resistance vanishes at even warmer temperatures.
	www.nist.gov /public_affairs/releases/magnetism_key.html (573 words)

	Breakthrough in high-temperature superconductivity
		The new results have shown for the first time that the mechanism of high-temperature superconductivity (when there is no resistance to the flow of electrical current) is actually coupled to the crystal lattice.
		Currently, the record temperature at which superconductivity is observed is -113 °C. Practical applications include superconducting magnets for MRI scanners and magnetic levitation trains.
		Chemical compounds that superconduct at temperatures >-238°C are known as “high-temperature superconductors”.
	www.physorg.com /news5893.html (918 words)

	current research: high-temperature superconductivity (Site not responding. Last check: 2007-11-05)
		The phenomenon of high-temperature superconductivity (HTS) is still far from being understood.
		In conventional superconductors it also plays a direct role in the superconductivity: an effective electron-electron interaction is mediated by the polarization of the atomic lattice by charge carriers.
		In the phenomenon of high-Tc superconductivity it is a controversial issue whether the lattice plays any direct role at all.
	www.pa.msu.edu /people/billinge/hts.html (305 words)

	UT Physics News: UT Physcists Probe High-Temperature Superconductivity in Nature
		The temperature where a material becomes a superconductor is called its transition, or critical, temperature (Tc).
		Although the consensus has been that phonons themselves are not enough to induce high-Tc superconductivity, what exactly is the "glue" that binds electrons for superconductivity is still a subject of controversy.
		Yet they become superconducting when either electrons or "holes"—a vacant electron position that behaves as if it were an electron with a positive charge—are added in a process called doping.
	www.phys.utk.edu /news/2006/news_07062006_dai.html (647 words)

	Encyclopedia: High-temperature superconductivity
		Cryogenics is the study of very low temperatures or the production of the same, and is often confused with cryobiology, the study of the effect of low temperatures on organisms, or the study of cryopreservation.
		The term high-temperature superconductor was initially employed to designate the new family of cuprate-perovskite ceramic materials discovered by J.G. Bednorz and K.A. Mueller in 1986.
		Yttrium barium copper oxide, or YBCO, chemical formula YBa2Cu3O7-δ, is a high-temperature superconductor with a superconducting temperature of 94K.
	www.nationmaster.com /encyclopedia/High_temperature-superconductivity (493 words)

	LinuxElectrons - Scientists Closing In On High-Temperature Superconductivity
		Scientists first observed superconductivity in materials chilled to certain “transition” temperatures very close to “absolute zero,” or zero degrees Kelvin (K), the coldest temperature possible, which is equal to minus 452 degrees Fahrenheit (°F).
		But more recent research has uncovered a class of so-called “high-temperature” superconductors that perform at temperatures as “warm” as 138 K. While still extremely cold by conventional standards, these higher temperatures are easier to achieve, making high-temperature superconductors more feasible for practical applications.
		Their test sample was a high-temperature superconducting compound containing the elements bismuth, strontium, calcium, copper, and oxygen, known as Bi-2212.
	www.linuxelectrons.com /article.php/2004022608203395 (603 words)

	MSEL Annual Report 1997: High Temperature Superconductivity
		The primary focus of the MSEL program is on bulk superconducting materials for wire and magnet applications.
		Database - A high temperature superconductor database has been developed in collaboration with the National Research Institute for Metals (NRIM) in Japan.
		The High Temperature Superconductor Database (HTSD) includes evaluated open-literature data on numerous physical, mechanical, and electrical properties of a variety of chemical systems.
	www.msel.nist.gov /mselannualreport97/hightemp.html (422 words)

	Fluid ''Stripes'' May Be Essential for High-Temperature Superconductivity
		The more barium, the more holes, and the greater the superconductivity – until the composition reaches a point where there is exactly one barium atom for every eight copper atoms: Then the superconductivity disappears.
		But trying to study these materials in their superconducting form is “like looking at the stripes on a waving flag from a great distance using soda bottles as binoculars,” Tranquada said.
		The scientists have not yet demonstrated experimentally how the stripes contribute to the high-temperature superconductivity, but Tranquada says the quest for such evidence is likely to generate great interest in the field.
	www.physorg.com /news147.html (929 words)

	Unraveling the Mystery of High-Temperature Superconductivity
		These materials conduct electricity with virtually no resistance at temperatures high enough to be cooled by liquid nitrogen (-196 degrees C, or -321 degrees F) instead of more costly helium.
		Studies at various national laboratories have led to discoveries concerning, for example, the relationships between magnetic behavior and superconductivity, and between material layering and current-carrying capability.
		Argonne also built the first superconducting motor and developed a process for welding lengths of wire in a way that maintains superconductivity.
	www.er.doe.gov /sub/accomplishments/Decades_Discovery/24-pf.html (372 words)

	HIGH TEMPERATURE SUPERCONDUCTIVITY
		Then, from various laboratories, came a series of announcements that superconductivity had been achieved at much higher temperatures, where cheaper cooling techniques could be used.
		Despite the problems, however, a significant amount of progress has been made, and high temperature superconductivity remains an area of research with enormous technological potential.
		In fact, CTF-manufactured biomagnetometers, which are used to detect minute magnetic fields in the human body, incorporate a conventional superconducting sensor that was developed in collaboration with the SFU surface physics laboratory.
	www.sfu.ca /~science/media/superconductor.html (672 words)

	Unlocking The Secrets Of High-Temperature Superconductors
		The more barium that is "doped" into the material, the more holes, and the greater the superconductivity - until the composition reaches a point where there is exactly one barium atom for every eight copper atoms, a state known as the 1/8 doping.
		Yet, it doesn't have superconductivity." Homes and other BNL researchers continue to tackle this mysterious problem in order to understand why a material that wants to be a superconductor is behaving like an insulator.
		Achieving this high barium concentration is extremely difficult and is the reason many scientists previously opted to use different but related materials for their research on superconducting stripes and other properties, Gu said.
	www.energy-daily.com /reports/Unlocking_The_Secrets_Of_High_Temperature_Superconductors_999.html (1572 words)

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