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Topic: Conventional superconductors

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Superconductivity

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	Superconductivity - Wikipedia, the free encyclopedia
		In conventional superconductors, superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase composed of correlated pairs of electrons.
		Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines.
		In a class of superconductors known as type II superconductors (including all known high-temperature superconductors), an extremely small amount of resistivity appears when an electrical current is applied in conjunction with a strong magnetic field (which may be caused by the electrical current).
	en.wikipedia.org /wiki/Superconductor (2566 words)

	Superconductivity (Site not responding. Last check: 2007-11-04)
		In conventional superconductors, superconductivity is caused by a force of attraction between certain conduction electronss arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase composed of correlated pairs of electrons.
		Superconductors are also quite willing to maintain a current with no applied voltage whatsoever, a property exploited in the coils of MRI machines, among others.
		Many stories attribute additional properties to their hypothetical superconductors, ranging from infinite heat conductivity in Niven's novels (real superconductors conduct heat poorly, though liquid helium has immense heat conductivity) to teleportation in the Stargate movie and TV series.
	www.sciencedaily.com /encyclopedia/superconductivity (2301 words)

	Superconductivity Article, Superconductivity Information (Site not responding. Last check: 2007-11-04)
		In conventional superconductors,superconductivity is caused by a force of attraction between certain conduction electrons arising from the exchange of phonons, which causes the conduction electrons to exhibit a superfluid phase composed of correlatedpairs of electrons.
		Superconductors are also quite willing to maintain a current with no applied voltage whatsoever,a property exploited in the coils of MRI machines, among others.
		The electrons are constantly colliding with the ions in the lattice, and during eachcollision some of the energy carried by the current is absorbed by the lattice andconverted into heat (which is essentially the vibrational kinetic energy of the lattice ions.) As a result, the energy carried by the current is constantlybeing dissipated.
	www.anoca.org /superconductors/field/superconductivity.html (2157 words)

	Unconventional superconductor - Wikipedia, the free encyclopedia
		Unconventional superconductors are materials that display superconductivity but that do not conform to BCS theory or its extensions.
		This is highly significant from the point of view of the technological applications of superconductivity, because liquid nitrogen is far less expensive than liquid helium, which is required to cool conventional superconductors down to their critical temperature.
		These include some that do not superconduct at high temperatures, such as the strontium-ruthenate oxide compounds, but that, like the high-temperature superconductors, are unconventional in other ways (for example, the origin of the attractive force leading to the formation of Cooper pairs may be different from the one postulated in BCS theory).
	en.wikipedia.org /wiki/Unconventional_superconductors (320 words)

	Superconductivity - Open Encyclopedia (Site not responding. Last check: 2007-11-04)
		As of 2001, the highest critical temperature found for a conventional superconductor is 39K for magnesium diboride (MgB
		In 1913, lead was found to superconduct at 7K, and in 1941 niobium nitride was found to superconduct at 16K.
		The next important step in understanding superconductivity occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect.
	open-encyclopedia.com /Superconductivity (2301 words)

	Oxford Physics - Oxford Physics - Condensed Matter Physics - Superconductors (Site not responding. Last check: 2007-11-04)
		Current theories range from quasi-particle models where high-Tc superconductors are similar to conventional superconductors and the pairing occurs between weakly interacting quasiparticles.
		superconductor is highly complex, including antiferromagnetic order, striped magnetism and spin-glass phases in addition to superconductivity, and it is thought that the presence of magnetic fluctuations is vital to the superconducting process.
		Organic superconductors are intrinsically anisotropic because of their layered structure and this has important consequences.
	www.physics.ox.ac.uk /CM/superconductors.htm (1681 words)

	Ceramics WebBook: WebHTS Help
		Superconductors are materials in which the electrical resistivity is zero when the temperature of the material is less than a critical temperature, Tc.
		Superconductors have been known only since the early part of the twentieth century [2].
		A conceptual understanding of all of the conventional superconductors was established in 1957 by the BCS theory of superconductivity [5].
	www.ceramics.nist.gov /srd/hts/WebHTSHelp.htm (2442 words)

	The Daily Californian (Site not responding. Last check: 2007-11-04)
		Superconductors, which allow for virtually unrestricted electrical conductivity, have a range of commercial and scientific applications, including very high-speed microprocessors and magnetic levitation trains.
		This "flexibility", or behaving like both a high-temperature and a low-temperature superconductor at the same time is interesting to scientists, as it broadens the range of temperatures at which a compound becomes a superconductor.
		As superconductors generally function only at extremely low temperatures near absolut zero, it has been the mission of many scientists to drive the temperature of superconductors higher, so that they can be mass produced more easily and have wider applications.
	www.dailycal.org /particle.php?id=9240 (536 words)

	Heat test sheds new light on nature of novel superconductors (Site not responding. Last check: 2007-11-04)
		STANFORD -- Exceedingly delicate measurements of the rate at which high temperature superconductors absorb heat are providing new evidence that the ability of these materials to conduct electric current without resistance has a fundamentally different basis from that of conventional superconductors.
		The results are consistent with, and significantly strengthen, the evidence that the electron-pair binding in high temperature superconductors takes a form that scientists call "d-wave." As a result, their work has received considerable interest within the scientific community since it was published last November in Physical Review Letters.
		The electron-pair binding force in conventional superconductors -- which have been known since 1911 but which operate only at temperatures lower than minus 200 degrees Celsius -- is the same in all directions.
	www.stanford.edu /dept/news/relaged/950321Arc5310.html (750 words)

	Inhaltsverzeichnisseite (Site not responding. Last check: 2007-11-04)
		Apart from the fact that the superconducting transition temperatures dramatically differ by orders of magnitude between these categories, probably the most significant distinction between conventional and unconventional superconductors is found in the symmetry of their order parameters.
		Conventional superconductors are well described by a so-called s-wave order parameter which implies isotropic attractive forces between electrons in all spatial directions.
		For anisotropic superconductors these experiments reveal exotic patterns, such as those shown in seen in the figures to the left, which serve as fingerprints for the underlying unconventional order parameter.
	physics.usc.edu /CCM/uncsup.htm (825 words)

	Press Release - 1999 Brockhouse Medal to Walter Hardy
		High-temperature superconductors were discovered in 1986 by physicists Georg Bednorz and Karl Müller, who were awarded the 1987 Nobel prize for their discovery.
		Conventional superconductors conduct electricity with no power loss indefinitely, but only at extremely low temperatures that are difficult and expensive to achieve.
		The extraordinary challenges posed by this unexpected phenomenon have also generated enormous scientific excitement and activity, as the way in which these new materials become superconductors is not understood, but may be quite different from that in conventional superconductors.
	www.cap.ca /awards/press/1999-hardy.html (693 words)

	News Release - Physicist's Yin Yang theory attracts attention - Feb 21, 2002 (Site not responding. Last check: 2007-11-04)
		High temperature superconductors conduct many more electrons in a shorter space of time than conventional superconductors, and can do so at a higher temperature (minus 200 to minus 173 Celcius).
		Ultimately, high temperature superconductors could be as revolutionary to electronics and to the transmission of electrical power as fibre optics was to telecommunications.
		Another advantage of high temperature superconductors is they don’t require liquid helium like their conventional counterparts to be cooled to their extremely low critical temperatures.
	www.sfu.ca /mediapr/print/news_releases/archives/news02210201.html (474 words)

	Run-of-the-mill compound becomes superstar: Science News Online, March 3, 2001
		Researchers have long dreamed of superconductors that would operate at room temperature, or 300 K. Such substances would revolutionize industry and other sectors of society by slashing the energy required to run machines while bettering their performance.
		Conventional superconductors, such as certain metal alloys, are used in commercial magnetic resonance imaging (MRI) machines and in research magnets.
		Decades of research have yielded no conventional superconductors with a critical temperature higher than 23 K. Since the late 1980s, the discovery of so-called ceramic high-temperature superconductors has diverted attention from conventional compounds.
	www.sciencenews.org /articles/20010303/fob5.asp (582 words)

	08.16.2004 - Vibrations in crystal lattice plays big role in high temperature superconductors
		A ceramic high temperature superconductor is actually a very poor metal, almost an insulator, at room temperature because electrons interact only slightly with the solid lattice (top), as represented by a slight depression in the crystal lattice.
		High temperature superconductors are almost always some type of copper oxide (cuprate) ceramic doped with a variety of elements, from bismuth, yttrium and lanthanum to strontium and calcium.
		The complex crystal structure of Bi-2212, a typical cuprate ceramic high temperature superconductor, showing two distinct alternating layers: the copper oxide layer (purple is copper, brown is oxygen) and the bismuth oxide layer (green is bismuth), interspersed with atoms of calcium (pink) and strontium (orange).
	www.berkeley.edu /news/media/releases/2004/08/16_Lanzara.shtml (1190 words)

	SFU News - Herbut attracts attention of peer - Feb 21, 2002 (Site not responding. Last check: 2007-11-04)
		Herbut and his fellow researchers in solid state physics (physics of solids, liquids, glass) are locked in a race to unravel the mystery of what causes high temperature superconductors to behave in a very metaphysical way.
		High temperature super—conductors conduct many more electrons in a shorter space of time than conventional superconductors, and can do so at a higher temperature (minus 200 to minus 173 Celsius).
		Their superior electrical conductivity makes it possible to accomplish the work of 10 wires in a conventional superconductor with one wire,” explains Herbut, an assistant professor of physics.
	www.sfu.ca /mediapr/print/sfu_news/sfunews02210208.html (471 words)

	Unconventional wisdom (March 2005) - News - PhysicsWeb
		In conventional superconductors, electrons pair up as a result of their interactions with vibrations of the crystal lattice known as phonons.
		In contrast, it is thought that the electron pairs in unconventional superconductors are formed as a result of interactions with magnetic fluctuations in the material.
		In a conventional or low-temperature superconductor the total orbital angular momentum of the two electrons in a Cooper pair is zero -- a so-called s-wave state.
	physicsweb.org /articles/news/9/3/17/1 (460 words)

	Physics Help and Math Help - Physics Forums - BCS theory
		These superconductors are called type-I. They are metals and are characterised by the Meissner effect, that is, in the superconductive state they actively counteract a surrounding magnetic field as long as its strength does not exceed a certain limit (fig.
		Now, high-Tc superconductors (which experimentally occur to be of type-II as far as their magnetic properties are concerned) seem not to be "conventional" superconductors.
		However, there are theoretical difficulties (in High-Tc superconductors) to determine the nature of the interaction which induces the paring of electrons: It may be that the lattice vibrations are not the right candidate for High-Tc superconductors.
	www.physicsforums.com /printthread.php?t=11739 (1943 words)

	Physics Today November 2001
		In conventional, noncuprate superconductors, the three themes are generally quite distinct.
		The current-carrying properties of all the grain boundaries in the cuprate superconductors are qualitatively similar.
		One approach is to use circuits made out of conventional superconductors in which Josephson junctions are connected in loops.
	www.aip.org /pt/vol-54/iss-11/p48.html (3689 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		In the standard BCS superconductors the Cooper-pair size xi_pair and the coherence length for the gap fluctuations xi_0 are of the same order, being both settled by the ratio between the Fermi velocity v_F and the gap amplitude Delta_0.
		A detailed study of the various length scales in these non conventional superconductors is then requested: in particular the effects of the d-wave symmetry of the gap and of the not small strength of the pairing interaction have to be taken into account.
		We show explicitly [2](in the s-wave case, but we do not expect significant differences for d-wave superconductors) that the coherence length xi_0 is effectively reduced to the order of a lattice spacing at finite density, while in the extreme diluted limit we recover the expected divergence for the coherence length of a weakly-interacting bosonic system.
	www.mpipks-dresden.mpg.de /~quantimp/quant-imp/abstracts/toschi.html (257 words)

	Physics Today September 2001
		In conventional superconductors, lattice vibrations push the electrons together into the superconducting state.
		superconductors are found poised on the edge of antiferromagnetism.
		Even iron itself, the archetypal ferromagnet, has recently been found to be a superconductor, albeit under such high pressure that it ceases to be ferromagnetic.
	www.physicstoday.org /pt/vol-54/iss-9/p16.html (1377 words)

	Superconductivity
		Rapidly, all the old experiments which had lead to the unifying theory of conventional superconductors were repeated.
		The cuprate crystal structures are much more complicated than the conventional superconductors, with typically four or five different elements per unit cell.
		In addition, there have also been discovered many electron-doped superconductors, with a phase diagram that is nearly the mirror image of the hole-doped materials.
	hoffman.physics.harvard.edu /research/SCintro.php (1119 words)

	Past Research (Site not responding. Last check: 2007-11-04)
		The discovery of superconductors caused a great deal of excitement because one can imagine many uses for a material that carries currents without resistance.
		My goal is to study the high temperature superconductors using a powerful microscope known as the scanning tunneling microscope (STM).
		arises in conventional superconductors because one has to provide enough energy to break a copper pair into distinct electrons.) Although the presence of the pseudo gap is well established, the origins of the gap as well as the details of the phase diagram associated with the gap are still a subject of debate.
	ph99.bc.edu /madhavan/PastResearchpage.htm (616 words)

	Probing superconductivity on the Nanoscale
		Davis and his colleagues set out to investigate this phenomenon directly at the atomic scale in a superconductor known as BSCCO (pronounced "bisko," for bismuth strontium calcium copper oxide), in order to determine what influence individual impurity atoms have on electronic structure in their immediate neighborhoods.
		All the highest-Tc superconductors found so far are copper oxide ceramics having the crystal structure of the mineral perovskite, with planes of copper and oxygen atoms (where superconductivity is thought to occur) interlayered with planes of other atoms.
		The electronic states of Cooper pairs in high-Tc superconductors are markedly different from those in conventional ones: the two electrons revolve around each other much faster and farther apart, as do their associated quasiparticles.
	enews.lbl.gov /Science-Articles/Archive/probing-superconductivity.html (1005 words)

	Ballistic phonons reveal strange attenuation in lead superconductor
		"Lead is a conventional superconductor with not-so-conventional properties," said Jim Wolfe, a UI professor of physics and a researcher at the university’s Frederick Seitz Materials Research Laboratory.
		The technique — which measures the spatial pattern of heat flux emanating from a point source — can probe anisotropies in the superconducting gap of conventional superconductors.
		To image phonons, Wolfe and his graduate student, Jonathan Short, use a laser pulse to generate thermal energy at a point on the surface of a supercooled crystal.
	www.eurekalert.org /pub_releases/2001-03/UoIa-Bprs-1503101.php (470 words)

	Graduate Brochure - Condensed Matter Theory (Site not responding. Last check: 2007-11-04)
		Superconductivity: In 1986, entirely new classes of superconductors were discovered with high transition temperatures compared to conventional superconductors.
		The superconducting state has a different symmetry, d-wave, from that in the conventional superconductors, which are s-wave.
		This leads to new phenomena and means that much of the conventional theory needs to be changed.
	www.phys.ufl.edu /GradBrochure/research/cmt.htm (569 words)

	ScienceWeek
		1) One view of the high-transition-temperature (high-Tc) copper oxide superconductors is that they are conventional superconductors where the pairing occurs between weakly interacting quasiparticles (corresponding to the electrons in ordinary metals), although the theory has to be pushed to its limit(1).
		The vortices form lattices of resistive material embedded in the non-resistive superconductor, and can reveal the nature of the ground state -- for example, a conventional metal or an ordered, striped phase -- which would have appeared had superconductivity not intervened, and which provides the best starting point for a pairing theory.
		Evidence for stripe correlations of spins and holes in copper-oxide superconductors.
	scienceweek.com /2003/sw030808-3.htm (702 words)

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