Superconductors

SUPERCONDUCTOR:   An element, inter-metallic alloy, or compound that will conduct electricity without  resistance below a certain temperature. Resistance is undesirable because it produces losses in the

energy flowing through the material. Once set is motion, electrical current will flow forever in a closed loop of superconducting material – making it the closest thing to perpetual motion in nature. Scientist refer to superconductivity as a “microscopic quantum phenomenon” . THE HISTORY OF SUPERCONDUCTORS:

Superconductors , materials that have no resistance to the flow of 

electricity, are one of the last great frontiers of scientific discovery. Not only have the limits of superconductivity not yet been reached, but the theories that explain superconductor behavior seem to be constantly under review. In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University (shown). When he cooled it to the temperature of liquid helium, 4 Kelvin (-452F, -269C), its resistance suddenly disappeared. The Kelvin scale represents an "absolute" scale of temperature. Thus, it was necessary to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of  superconductivity. superconductivity. Later, in 1913, he won a Nobel Prize in physics for his research in this area. °

Next great milestone in understanding how matter behaves at extreme cold temperatures occurred in 1933. German researchers Walther Meissner (above) and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field (below graphic). A magnet moving by a conductor induces currents in the conductor. This is the principle on which the electric generator operates. But, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material causing the magnet to be repulsed. This phenomenon is known as strong diamagnetism and is today often referred to as the "Meissner effect" (an Walther Meissner eponym). The Meissner effect is so strong that a magnet can actually be levitated over a superconductive material.

In subsequent decades other superconducting metals, alloys and compounds were discovered. In 1941 niobium-nitride was found to superconduct at 16 K. In 1953 vanadium-silicon displayed superconductive superconductive properties at 17.5 K. And, in 1962 scientists at Westinghouse developed the first commercial superconducting wire, an alloy of niobium and titanium (NbTi). High-energy, particle-accelerator electromagnets made of copper-clad niobium-titanium were then developed in the 1960s at the Rutherford-Appleton Laboratory in the UK, and were first employed in a superconducting superconducting accelerator at the Fermilab Tevatron in the US in 1987. °

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The first widely-accepted theoretical understanding of superconductivity was advanced in 1957 by American physicists John Bardeen, Leon Cooper, and John Schrieffer (above). Their Theories of  Superconductivity became know as the BCS theory - derived from the first letter of each man's last name - and won them a Nobel prize in 1972. The mathematically-complex BCS theory explained superconductivity at temperatures close to absolute zero for elements and simple alloys. However, at higher temperatures and with different superconductor systems, the BCS theory has subsequently subsequently become inadequate to fully explain how superconductivity is occurring. Another significant theoretical advancement came in 1962 when Brian D. Josephson (above), a graduate student at Cambridge University, predicted that electrical current would flow between 2 superconducting materials - even when they are separated by a non-superconductor or insulator. His prediction was later confirmed and won him a share of the 1973 Nobel Prize in Physics. This tunneling phenomenon is today known as the "Josephson effect" and has been applied to electronic devices such as the SQUID, an instrument capabable of detecting even the weakest magnetic fields. (Below SQUID graphic courtesy Quantum Design.) Bria Briann Jose Jose hson hson

The 1980's were a decade of unrivaled discovery in the field of superconductivity. In 1964 Bill Little of Stanford University had suggested the possibility of organic (carbon-based) superconductors. The first of these theoretical superconductors was successfully synthesized in 1980 by Danish researcher Klaus Bechgaard of the University of Copenhagen and 3 French team members. (TMTSF)2PF6 had to be cooled to an incredibly cold 1.2K transition temperature (known as Tc) and subjected to high pressure to superconduct. But, its mere existence proved the possibility of "designer" molecules - molecules fashioned to perform p erform in a predictable way. w ay. Then, in 1986, a truly breakthrough discovery was made in the field of superconductivity. Alex Müller and Georg Bednorz (Photo), researchers at the IBM Research Laboratory in Rüschlikon, Switzerland, created a brittle ceramic compound that superconducted at the highest temperature then known: 30 K. What made this discovery so remarkable was that ceramics are normally insulators. They don't conduct electricity well at all. So, researchers had not considered them as possible hightemperature superconductor candidates. The Lanthanum, Barium, Copper and Oxygen compound that Müller and Bednorz synthesized, behaved in a not-as-yetunderstood way. The discovery of this first of the superconducting copper-oxides (cuprates) won the 2 men a Nobel Prize the following year. It was later found that tiny amounts of this material were actually superconducting at 58 K, due to a small amount of lead having been added as a calibration standard - making the discovery even more noteworthy. °

Müller and Bednorz' discovery triggered a flurry of activity activit y in the field of superconductivity. superconductivity. Researchers around the world began "cooking" up ceramics of every imaginable combination in a Page 2 of 31

quest for higher and higher Tc's. In January of 1987 a research team at the University of AlabamaHuntsville substituted Yttrium for Lanthanum in the Müller and Bednorz molecule and achieved an incredible 92 K Tc. For the first time a material (today referred to as YBCO) had been found that would superconduct at temperatures warmer than liquid nitrogen - a commonly available coolant. Additional milestones have since been achieved using exotic - and often toxic - elements in the base perovskite ceramic. The current class (or "system") of ceramic superconductors with the highest transition temperatures are the mercuric-cuprates. The first synthesis of one of these compounds was achieved in 1993 at the University of Colorado and by the team of A. Schilling, M. Cantoni, J. D. Guo, and H. R. Ott of Zurich, Switzerland. The world record Tc of 138  K  is now held by a thallium-doped, mercuric-cuprate comprised of the elements Mercury, Thallium, Barium, Calcium, Copper and Oxygen. The Tc of this ceramic superconductor was confirmed by Dr. Ron Goldfarb at the National Institute of Standards and Technology-Colorado in February of 1994. Under extreme pressure its Tc can be coaxed up even higher - approximately 25 to 30 degrees more at 300,000 atmospheres. atmospheres. The world record Tc of 138 K °    °    

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The first company to capitalize on high-temperature superconductors was Illinois Superconductor (today known as ISCO International), formed in 1989. This amalgam of government, private-industry and academic interests introduced a depth sensor for medical equipment that was able to operate at liquid nitrogen temperatures (~ 77K). In recent years, many discoveries regarding the novel nature of superconductivity have been made. In 1997 researchers found that at a temperature very near absolute zero an alloy of gold and indium was both a superconductor and a natural magnet. Conventional wisdom held that a material with such properties could not exist! Since then, over a half-dozen such compounds have been found. Recent years have also seen the discovery of the first high-temperature superconductor that does NOT contain any copper (2000), and the first all-metal perovskite superconductor superconductor (2001). Also in 2001 a material that had been sitting on laboratory shelves for decades was found to be an extraordinary new superconductor. Japanese researchers measured the transition temperature of magnesium diboride at 39 Kelvin - far above the highest Tc of any of the elemental or binary alloy superconductors. While 39 K is still well below the Tc's of the "warm" ceramic superconductors, subsequent refinements in the way MgB 2 is fabricated have paved the way for its use in industrial applications. Laboratory testing has found MgB 2 will outperform NbTi and Nb3Sn wires in high magnetic field applications like MRI. °

Though a theory to explain high-temperature superconductivity still eludes modern science, clues occasionally appear that contribute to our understanding of the exotic nature of this phenomenon. In 2005, for example, Superconductors.ORG discovered that increasing the weight ratios of alternating planes within the layered perovskites can often increase Tc significantly. This has led to the discovery of more than 40 new high-temperature superconductors, including a candidate for a new world record. The most recent "family" of superconductors superconductors to be discovered is the "pnictides". These ironbased superconductors were first observed by a group of Japanese researchers in 2006. Like the high-Tc copper-oxides, the exact mechanism that facilitates superconductivity in them is a mystery. However, with Tc's over 50K, a great deal of excitement has resulted from their discovery. Researchers do agree on one thing: discovery in the field of superconductivity is as much serendipity as it is science.

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SUPERCONDUCTOR TERMINOLOGY   AND THE NAMING SCHEME

To heat and then slowly cool a material to reduce brittleness. Annealing of ceramic superconductors usually follows sintering and is done in an oxygen-rich atmosphere to restore oxygen lost during calcination. The oxygen content of a ceramic superconductor is critical. For example, YBCO with 6.4 atoms of oxygen will not superconduct. But YBCO with 6.5 atoms will.  Anneal:

A state of  matter where adjacent ions in a material are aligned in opposite or "anti-parallel" arrays. Such materials display almost no response to an external magnetic field at low temperatures and only a weak attaction at higher temperatures. There is evidence that anti-ferromagnetism in the copper oxides plays a role in the formation of Cooper pairs and, thus, in facilitating a superconductive state in some compounds.  Anti-ferromagnetism:

The first widely-accepted theory to explain superconductivity put forth in 1957 by John Bardeen, Leon Cooper, and John Schreiffer. The theory asserts that, as electrons pass through a crystal lattice, the lattice deforms inward towards the electrons generating sound packets known as "phonons". These phonons produce a trough of positive charge in the area of deformation that assists subsequent electrons in passing through the same region in a process known as phononmediated coupling. This is analogous to rolling a bowling ball up the middle of a bed. 2 people, one lying on each side of the bed, will tend to roll toward the center of the bed, once the ball has created a depression in the mattress. And, a 2nd bowling ball, placed at the foot of the bed, will now, quite easily, roll toward the middle.   BCS Theory:

Superconducting borocarbides are compounds containing both boron and carbon in combination with rare-earth and transition elements; some of which exhibit the unusual ability to return to a normal, non-superconductive state at temperatures below Tc. For more on this, click here.  Borocarbides:

An acronym for a ceramic superconductor system containing the elements Bismuth, Strontium, Calcium, Copper and Oxygen. Typically, a small amount of lead is also included in these compounds to promote the highest possible Tc. BSCCO has probably found the widest acceptance among high-Tc superconductor superconductor applications due to its unique properties. BSCCO compounds exhibit both an intrinsic Josephson effect and anisotropic (directional) behavior. You can view a list of BSCCO compounds on the "Type 2" page.  BSCCO:

Ceramic superconductors are inorganic compounds formed by reacting a metal with oxygen, nitrogen, carbon or silicon. The best-known of these are the copper-perovskites. Ceramics are typically hard, brittle, heat-resistant materials formed by a process known as solidstate reaction. Ceramics:

In superconductors, charge reservoirs are the layers that may control the oxidation state of adjacent superconducting planes (even though they themselves are not superconducting). superconducting). In the layered cuprates, these consist of copper-oxide chains. Charge Reservoirs:

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A class of molybdenum chalcogenides (compounds containing Group VI elements S, Se or Te along with molybdenum and a positively charged metal ion) - named for Roger Chevrel of the University of Rennes, whose research brought them to the attention of the scientific community in the early 1970's. Recently, the Superconductivity Group at the University of Durham (UK) reported a novel fabrication technique that increases Bc2 (upper critical field) in the chevrel PbMo6S8 from 50 T in bulk materials up to > 100 T. Click HERE to read a [technical] writeup on this (as a PDF file). Or click HERE to see a short list of some of these compounds alongside their Tc's. Chevrel (phases):

The size of a cooper pair - representing the shortest distance over which superconductivity superconductivity can be established in a material. This is typically t ypically on the order of 1000Å; although it can be as small as 30Å in the copper oxides. Coherence Length:

Two electrons that appear to "team up" in accordance with theory - BCS or other - despite the fact that they both have a negative charge and normally repel each other. (Named for Leon Cooper.) Below the superconducting transition temperature, paired electrons form a condensate - a macroscopically occupied single quantum state - which flows without resistance. However, since only a small fraction of the electrons are paired, the bulk does not qualify as being a "bose-einstein condensate". condensate". Click here to see an animation of a cooper pair. Cooper Pair:

An acronym for "diamond anvil cell". Often the Tc of a superconductor can be coaxed upward with the application of high pressure. The DAC is used to accomplish this in the laboratory. A DAC is composed of 2 specially-cut diamonds and a stainless steel gasket. The gasket goes between the diamonds and seals a small chamber in which a fluid is placed. Since neither the diamonds nor the liquid will compress, hydrostatic hydrostatic forces in excess of a million atmospheres can be brought to bear on a sample suspended within the fluid. Click here to see a graphic of a DAC.  DAC:

 Diamagnetism: The ability of a material to repel r epel a magnetic field. Many naturally-occurring substances (like water, wood and paraffin, and many of the elements) exhibit weak  diamagnetism. Superconductors Superconductors exhibit strong diamagnetism below Tc. In a few rare compounds, a material may become superconductive superconductive at a higher temperature than the point at which diamagnetism di amagnetism appears. appears. But,

as a rule, the onset of strong diamagnetism is one of the most reliable ways to ascertain when a material has become superconductive superconductive

A form of electron pairing in which the electrons travel together in orbits resembling a four-leaf clover. Wave functions help theoreticians describe (and predict) electron behavior. The d-wave models have gained substantial support recently over s-wave pairing as the mechanism by which high-temperature superconductivity might be explained  D-Wave:

This is the energy required to break up a pair of electrons. According to BCS theory, the formula for determining the energy gap (in meV) is E g=7/2 KTc. Where K = Boltzmann's constant (8.62e-5 eV/K). And where Tc is the critical transition temperature in Kelvin. Since electron-pairing is universally agreed to be the method by which superconductivity occurs, this is the amount of energy required to disrupt the superconducting state.  Energy Gap:

An acronym for "Electron Spin Resonance" (also EPR: Electron Paramagnetic Resonance). This is another mechanism by which superconductivity might be explained in some materials. Simply put, ESR is the response of electrons to electromagnetic radiation or magnetic fields at discrete frequencies. Electrons, as they move, create tiny magnetic moments. Nearby electrons are influenced either beneficially or adversely. When the moments are complementary, the electrons become paired and can help each other move through a crystal lattice.  ESR:

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Ferrites are ceramics with magnetic properties. They are included on this page because many of the same elements used in ferrites (e.g. Ba, Sr, Tm, O) are also key constituents in ceramic superconductors. This may be an important clue in understanding high-temperature superconductivity.  Ferrite:

A state wherein a material exhibits magnetization through the alignment of internal ions (neighboring magnetic moments). This contrasts with paramagnetism, which is temporary, much weaker and results from unpaired electrons.  Ferromagnetism:

A configuration created when flux lines from a strong magnetic field try to penetrate the surface of a Type 2 superconductor. The tiny magnetic moments within each resulting vortex repel each other and a periodic lattice results as they array themselves in an orderly fashion.  Flux-Lattice:

The smallest magnetic flux (flux quantum) that exists in nature. Just as electrons are quantized charge, fluxons are a quantized flux. The term is used in association with vortices, which result from magnetic fields penetrating Type 2 superconductors in single fluxon quanta. Click here to view a hollographic depiction of waves of fluxons on the surface of superconducting Niobium.  Fluxon:

lux-Pinning: The phenomenon where a magnet's lines of

force (called flux) become trapped or "pinned" inside a superconducting material. This pinning binds the superconductor to the magnet at a fixed distance. Flux-pinning is only possible when there are defects in the crystalline structure of the superconductor (usually resulting from grain boundaries or impurities). Flux-pinning is desirable in high-temperature ceramic superconductors in order to prevent "flux-creep", which can create a pseudo-resistance and depress Jc and Hc. Click here to see a superconductor suspended in air by flux-pinning. The most common method of determining the Tc of a superconductor. Wires are attached to a material at four points with a conductive adhesive. Through two of these points a voltage is applied and, if the material is conductive, a current will flow. Then, if any resistance exists in the material, a voltage will appear across the other two points in accordance with Ohm's law (voltage equals current times resistance). When the material enters a superconductive state, its resistance drops to zero and no voltage appears across the second set of points. By using the four-point method, instead of just two points, resistance in the adhesive and wires can be ignored; as the second set of points do not themselves conduct any current and can, therefore, only reflect what voltage exists across the body of the material.  Four-point Probe:

  Hall Effect: When

a magnetic field is applied perpendicularly to a thin metal film or semiconductor film that is conducting an electric current, a small voltage will appear perpendicular to the axis of both the t he film and the magnetic field. This voltage is proportional to the strength of the t he applied field. However, the output is typically not linear. The Hall resistance (the ratio of the Hall voltage to the current) changes in steps, pursuant to the laws of quantum mechanics. This is known as the Integral Quantum Hall Effect or just Quantum Hall Effect. Discovered in 1879, the Hall effect was named for its discoverer Edwin H. Hall, a graduate student at Johns Hopkins University. The scientific notation representing the "critical field" or maximum magnetic field that a superconductor can endure before it is "quenched" and returns to a non-superconducting state. Usually a higher Tc also brings a higher Hc.  Hc:

Compounds containing the elements cerium, ytterbium or uranium; whose (inner shell) conduction electrons often have effective masses (called quasiparticle masses) several hundred times as great as that of a "free" (normal) electron mass. This gives them what's   Heavy Fermions:

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known as a low "Fermi energy" and makes them unlikely unli kely - and unusual - superconductors. Research Research suggests cooper-pairing in heavy fermion systems arises from the magnetic interactions of the electron spins.  Hole: A positively-charged vacancy vacancy within a crystal cr ystal lattice resulting from the shortage of

an electron in that region. Holes are typically t ypically induced by doping a material with an impurity. However, they can also be synthesized electronically with devices like the field-effect transistor (FET). Modern electronic devices rely heavily on holes (as p-type semiconductors) to function. There is evidence that the holes of hypocharged oxygen in charge-reservoirs are, in fact, what makes possible high-temperature superconductivity superconductivity in the layered cuprates.  HTS: An acronym for "High-Temperature Superconductor" (or Superconductivity). There is

no widely-accepted temperature that separates HTS from LTS (Low-Temperature Superconductors). Superconductors). However, all the superconductors known before the 1986 discovery of the superconducting oxocuprates would be classified LTS. The barium-lanthanum-cuprate fabricated by Müller and Bednorz, with a Tc of 30K, is generally considered to be the first HTS material. Certainly any compound that will superconduct superconduct above the boiling point of liquid nitrogen (77K) would be HTS. Hysteresis, as it applies to a superconductor, relates to the dynamic response of a superconductor to a strong magnetic field impinged upon it. As the strength of a nearby magnetic field (H) increases, the critical transition temperature (Tc) of a superconductor superconductor will decrease. And, at some point superconductivity will completely disappear, as it becomes "quenched". However, as the magnetic field is gradually withdrawn, the superconductor may  NOT  immediately return to a superconductive state. Herein lies the hysteresis. The graph of H-vs-Tc is different retreating than it is advancing (creating a "loop" shape). This fact must be weighed carefully in high-current applications where the superconductor superconductor Hc may, even briefly, be exceeded; as significant power losses can result.   Hysteresis (loop):

Infinite layer compounds have no clear separation between molecules. Rather than electrostatic bonding between discrete molecules to form a bulk crystalline aggregate, all the atoms are bound together by covalent or co-ionic bonding to form the equivalent of one huge molecule. (Ba,Sr)CuO2 and Na2Ba6Si46 are examples of "infinite layer" or "infinite network" superconductor superconductor compounds.  Infinite layer:

The influence atomic mass contributes to the critical transition temperature of a superconductor. For example, 203.4Hg has a Tc of 4.126K. While 198Hg has a Tc of 4.177K. Since both forms of mercury have the same lattice structure, this difference in Tc can be attributed solely to the difference in mass. To learn more, click here.  Isotope Effect:

The scientific notation representing the "critical current density" or maximum current that a superconductor can carry. Also note that, as the current flowing through a superconductor increases, the Tc will usually decrease.  Jc:

A phenomenon named for Cambridge graduate student Brian Josephson, who predicted that electrons would "tunnel" through a narrow (<10 angstroms) non-superconducting region, even in the absence of an external voltage. In a normal conductor, electrical current only flows when there's a voltage differential and contiguous electrical connection. It has been theorized that the Josephson Effect arises from the incoherent phase relationships between superconducting electrons in the two (separated) superconductors. superconductors. The AC Josephson Effect is where the current flow oscillates as an external magnetic field impinged upon it increases beyond a critical value. [at a frequency of 2eV/h, where e is the electron charge, V   Josephson Effect (also DC Josephson Effect):

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is the voltage that appears, and h is Planck's constant] Sidebar: This oscillation frequency has, in fact, resulted in an upward revision of Planck's constant from 6.62559e-34 to 6.626196e-34. 6.626196e-34. A thin layer of insulating material sandwiched between 2 superconducting layers. Electrons "tunnel" through this non-superconducting region in what is known as the "Josephson effect" (see above). Sidebar: The standard volt is now defined as the voltage required to produce a frequency of 483,597.9 GHz in a Josephson Junction.   Josephson Junction:

A scale of temperature measurement that starts at "absolute zero", the coldest theoretical temperature attainable. (Named for Lord William Wil liam Thomson Kelvin.)  Kelvin:

Exhibiting diamagnetic properties to the total exclusion of all magnetic fields. (Named for Walther Meissner.) This is a classic hallmark of superconductivity and can actually be used to levitate a strong rare-earth magnet. To see a movie of a magnet being levitated by a superconductor, click here.   Meissner Effect:

 Mott Transition: The

Mott transition is the shift from an insulating to a metallic state in a material. The high- temperature copper oxides are composed of CuO2 planes that are separated from each other by ionic "blocking layers". Although it has one conduction electron (or hole) per Cu site, each CuO2 plane is originally insulating because of the large electron correlation. That behavior is typical of the Mott insulator state, in which all the conduction electrons are tied to the atomic sites. The superconducting state emerges when holes from the blocking layers dope the CuO2 layers in a way that alters the t he number of conduction electrons and triggers the Mott transition. Researchers believe that the strong antiferromagnetic correlation, which originates in the Mottinsulating CuO2 sheets and persists into the metallic state, could be a possible mechanism of hightemperature superconductivity. (courtesy Science Week ) Organic superconductors are a sub-class of organic conductors that include molecular salts, polymers and pure carbon systems (including carbon nanotubes and C 60 compounds). They may also be referred to as "molecular" superconductors. They are typically large, carbon-based molecules of 20 or more atoms, consisting of a planar organic molecule and a nonorganic anion. For a non-technical write-up on organics, click here. Or, for a more technical paper on this subject, click here. Organics:

This term relates to how deeply a magnetic field will penetrate the surface of a superconductor. An external magnetic field impinged upon a Type 2 superconductor will decay exponentially into the surface based on the paired electron density within the superconductor (only a small fraction of the electrons are in a superconductive state). The "London" name comes from brothers F. London and H. London, who in 1935 created a theoretical model of superconductivity. For a more technical explanation and the actual formula to calculate penetration depth, click here.   Penetration Depth (also London Penetration Depth):

A large family of crystalline ceramics that derive their name from a mineral known as a perovskite. They are the most abundant minerals on earth and have a metal-to-oxygen ratio of approximately 2-to-3. Copper-oxide superconductors are layered perovskites. The perovskite name comes from Russian mineralogist Count Lev Aleksevich von Perovski.  Perovskites:

 Phase-Slip (also Quantum Phase-Slip): A point where a material in i n a superconductive state

spontaneously changes from one state to another, generating a topological "defect". This defect causes paired electrons to become "out of step" with each other, producing a voltage and, ergo, nonzero electrical resistance. This phenomenon has been observed in ultra-thin wires less than a few tens-of-nanometers in diameter. Though bulk superconductivity may persist (T
consequence of phase slip is a lower current-carrying state. A similar phenomenon occurs in Josephson Junctions. A term referring to the method by which Tc can often be increased by adjusting the relative weights of alternating layers in copper-oxide superconductors. The greatest improvements usually occur when making the insulating layers heavy/light OR the CuO2 planes heavy/light - but not both. Click HERE to read more about this discovery.  Planar Weight Disparity (PWD):

The phenomenon where a thin film of non-superconductive material in close proximity with a superconductor takes on superconductive properties. The Josephson junction is a device that takes advantage of this phenomenon. The Inverse Proximity Effect is where just the opposite occurs. A non-superconductive metal can enhance the Tc of an adjacent superconductor. This inverse effect has been observed with silver and lead.   Proximity Effect:

A rare form of electron pairing in which two electrons travel together in spherical orbits; with both having the same direction of rotation. rotati on. (See "D-Wave" explanation above.)  P-Wave:

Quasiparticle: A bare particle that is "dressed" or "clothed" by a cloud of other surrounding

particles. Quasiparticles behave similarly to bare (normal) particles, but usually have a larger effective mass due to this cloud moderating interactions with other particles. The phenomenon where superconductivity in a material is suppressed; usually by exceeding the maximum current the material can conduct (Jc) or the maximum magnetic field it can withstand (Hc). Quench:

A condition where a material retreats from its superconductive state and then re-enters it. This can be caused by a strong external magnetic field that dynamically exceeds the Hc of the material and/or is mis-aligned (in the case of some organic superconductors ), a discordant temperature below Tc (in the case of some borocarbides), or by Jc hysteresis (momentarily exceeding the critical current density, causing the Tc to shift downward).  Re-entrant (behavior):

The opposition of a material to the flow of electrical current through it. Energy lost due to resistance is a result of vibrations at the molecular level and manifests itself as heat in proportion to the square of the current flow. In a superconductor all resistance disappears below a certain temperature. However, this applies only to direct current (DC) electricity. Other types of  losses result when transporting alternating current (AC). Examples of this include hysteresis, reactive-coupling and radiational losses. In the new high-temperature ceramic superconductors, the power loss in applications like transmission lines is inversely proportional to the critical current density for low magnetic field applications. This limitation can be compensated for to some degree by increasing the ratio of voltage to current. In Type 2 superconductors carrying high-frequency alternating current, "skin effect" losses also result as the energy tends to migrate to the surface where the conductive medium is incontiguous, producing a pseudo-resistance. pseudo-resistance. In some materials the amount of resistance may also depend on the direction of current flow (anisotropic resistivity) and/or presence of an external magnetic field (hall effect).  Resistance:

Room-temperature Superconductor: There are NO confirmed room-temperature superconductors superconductors (as was once reported for lithium-beryllium-hydride lit hium-beryllium-hydride and for lead-silver-carbonate). However, it has been theorized that a metallic form of hydrogen might  be a room-temperature superconductor. In 1996 physicists at Lawrence Livermore Laboratory were able to briefly create metallic hydrogen. But, its existence was fleeting and no measurement of the Meissner effect was possible. Zero resistance has been observed at room temperatures in ballistic quantum wire. Page 9 of 31

However, having one-dimensional geometry, this wire does not exhibit the Meissner effect, except when configured as a closed loop. Sinter: The process of heating a material to just below its melting melti ng point. An extended period

of sintering is the method by which the constituent components of a ceramic superconductor are combined in a solid-state reaction. Since ceramic superconductors are inherently brittle, sintering helps promote intergranular bonding and hardness. A superconducting loop interrupted in 2 places by Josephson junctions. When sufficient electrical current is conducted across the squid body, a voltage is generated proportional to the strength of any nearby magnetic field. The SQUID, an acronym for Superconducting QUantum Interference Device, is the most sensitive detector known to science SQUID:

Stripes are microscopic rivers of charge that flow across the surface of a Type 2 superconductor. It is theorized that stripes encourage "holes" to pair up and, as such, may play a role in facilitating charge transfer. Recently, at the Stripes 2000 conference in Rome, Italy, it was shown that there exists a critical value of micro-strain that must be exerted upon the CuO 2 planes for stripes to form. Click here to learn more. Stripes:

Superconductor: An element, inter-metallic alloy, or compound that will

conduct electricity without resistance below a certain temperature. However, this applies only to direct current (DC) electricity and to finite amounts of current. All known superconductors superconductors are solids. None are gases or liquids. And all require extreme cold to enter a superconductive state. Once set in motion, current will flow forever in a closed loop of superconducting material - making it the closest thing to perpetual motion in nature. Scientists refer to superconductivity as a "macroscopic quantum phenomenon". In addition to being classified Type 1 and Type 2, superconductors can be categorized further by their dimensionality. Most are 3-D. But some compounds, like surface-doped NaWO3 and some organic superconductors are 2-D. Li 2CuO2 and single-walled carbon nano-tubes have shown rare 1-D superconductivity. In addition to repelling magnetic fields, enhanced thermal conductivity, higher optical reflectivity and reduced surface friction are also properties of  superconductors. superconductors. The term "superconductor" is also used in some instances to refer to materials that have near infinite thermal conductivity - such as carbon nanotubes. However, on this website it is used in the context of electrical conductivity only. A measure of the relative amount of induced magnetism in a material. Magnetic susceptibility is often used in lieu of resistance measurements to determine the transition temperature of a superconductor. Although, on occasion, the two techniques produce very different Tc's. In a typical superconductor, the (arbitrary) value of susceptibility will change from zero to a negative number as the temperature drops through Tc. However, in some materials it changes from positive to negative, as paramagnetism yields to diamagnetism. d iamagnetism. Susceptibility:

S-Wave: A form of electron pairing in which the electrons travel together in spherical orbits,

but in opposite directions. (See "D-Wave" explanation above.)

The scientific notation representing the critical transition temperature below which a material begins to superconduct. The sudden loss of resistance in a superconductive medium may occur across a range as small as 20 millionths of a degree or, in the case of some stoichiometrically imperfect compounds, tens of degrees. Click here to see a graphic example. ("Tc" is not to be confused with the atomic symbol for Technetium.) Tc:

A method of fabricating ceramic superconductors to more precisely control the growth of the crystalline structure to eliminate grain boundaries and achieve a Thin Film (Deposition):

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desired Tc. This can involve Pulsed-Laser Deposition (PLD) or Pulsed-Electron Deposition (PED) of the material. A variation of this technique can be used to increase the Tc of a superconductor by growing it on a supporting material with a smaller interatomic spacing. The supporting material acts as a molecular "girdle" to compress the atomic lattice of the superconductor, thereby raising its transition temperature. Superconductive Superconductive tape is made using thin film fil m deposition technology. As it applies to superconductivity, translational symmetry is where the process of charge transfer is repeated exactly as the charge carriers (paired electrons) traverse the solid. In a normal conductor, latent heat continuously vibrates the atomic lattice, deflecting mobile free electrons and preventing "perfect" translational symmetry. In a superconductor superconductor this scattering tendency is overcome. Translational Symmetry:

A nebulous term used to describe alkali metal tungstenates, vanadates, molybdates, titanates and niobates. The term was originally coined to describe Na xWO3 compounds; the crystals of which look much like the copper-tin alloy known as bronze. There have been reports of superconductivity as high as 91K for a surface-doped sodium tungsten-bronze. This material was the first high-temperature superconductor superconductor discovered that does not contain any copper. Tungsten-bronze:

Ultraconductor: Materials known as ultraconductors™ ultr aconductors™ display room-temperature resistance orders of magnitude lower  than the best metallic conductors. Examples of these materials

many include oxidized atactic polypropylene (OAPP) and other polymers. Since ultraconductor™ is a colloquial term, these materials might better be described as "hyperconductors". The Meissner effect cannot be confirmed in them, but strong (giant) diamagnetism is in evidence. Some of them may actually find acceptance in high-current applications ahead of superconductors as a result of  their low losses at ambient temperatures and pressures The process by which a quasiparticle becomes more like a bare (normal) particle. It is theorized this may be a driving force behind superconductivity, as undressed electrons are significantly lighter and can, thus, conduct current more readily. To learn more, click here. Undressing:

A unit cell is the smallest assemblage of atoms, ions, or molecules in a solid, beyond which the structure repeats to form the 3-dimensional crystal lattice. Unit Cell:

Swirling tubes of electrical current induced by an external magnetic field into the surface of a superconducting superconducting material that represent a topological t opological singularity in the wavefunction. These are particularly evident in Type 2 superconductors during "mixed-state" behavior when the surface is just partially superconducting. Superconductivity is completely suppressed within these volcano-shaped structures. Recent research suggests that flux vortices may NOT possess quantum values (equal to multiples of Planck's constant divided by 2 times electron charge). But may instead have but a tiny fraction of the basic unit of magnetism. The movement of  vortices can produce a pseudo-resistance and, as such, is undesirable. While superconductivity is a "macroscopic" phenomenon, vortices are a "mesoscopic" phenomenon. (See the graphic at the top of this page.) Vortices (plural of vortex):

An acronym for a well-known ceramic superconductor composed of Yttrium, Barium, Copper and Oxygen. This was the first truly "high temperature" ceramic superconductor discovered; having a transition temperature well above the boiling point of liquid nitrogen - a commonly available coolant. Its actual molecular formula is YBa 2Cu3O7, making it a "1-2-3" superconductor. YBCO compounds exhibit d-wave electron pairing. The patent for YBCO is held by Lucent Technologies. (You can view a list of the best-performing 1-2-3 compounds on the "Type 2" page.) YBCO:

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With the discovery of the ceramic superconductors, came a need for a classification system to describe structure types. The cuprate superconductors all have blocks of conducting CuO 2 planes, alternating with insulating, spacing and separating layers. This makes possible a systematic  Naming Scheme that allows for identification and comparison. The scheme chosen uses four numbers. The first denotes the number of  insulating layers between adjacent conducting blocks. The second represents the number of  spacing layers between identical CuO2 blocks. The third gives the number of  layers that separate adjacent CuO 2 planes within the conducting block . And, the fourth is the number of CuO 2 planes within a conducting block . Using the TlBa2Ca2Cu3O9 molecule depicted at left as an example, there is 1 insulating TlO layer, 2 spacing BaO layers, 2 separating Ca layers, and 3 conducting CuO 2 planes - making it a "1223" type. t ype. There are also occasionally letters of the alphabet in the 5th and 6th positions. Suffixes like "T*", "C", and "F" describe to researchers structure detail in the oxygen positions. To further complicate matters, several of the more popular structures have names that do NOT follow the 4-number scheme. For example, the compound Y 1Ba2Cu3O7 is often referred to by the 3-number name "123". This delineates the number of metal atoms (the stoichiometry) - without regard to atom location - within the structure. Using the 4-number scheme, it would be classified a "1212".

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 A TYPICAL SUPERCONDUCTORS SUPERCONDUCTORS  AND THE FUTURE

As if ceramic superconductors were not strange enough, even more mysterious superconducting superconducting systems have been discovered. One is based on compounds centered around the "Fullerene" . The fullerene name comes from the late designer-author Buckminster Fuller. Fuller was the inventor of the geodesic dome, a structure with a soccer ball shape. The fullerene also called a buckminsterfullerene or "buckyball" - exists on a molecular level when 60 carbon atoms join in a closed sphere. When doped with one or more alkali metals the fullerene becomes a "fulleride" and has produced Tc's ranging from 8 K for Na2Rb0.5Cs0.5C60 up to 40 K for Cs 3C60. In 1993 researchers at the State University of New York at Buffalo reported Tc's between 60 K and 70 K for C-60 doped with the interhalogen i nterhalogen compound compound ICl. Fullerenes, like ceramic superconductors, are a fairly recent discovery. In 1985, professors Robert F. Curl, Jr. and Richard E. Smalley of Rice University in Houston and Professor Sir Harold W. Kroto of the University of Sussex in Brighton, England, accidentally stumbled upon them. The discovery of superconducting alkali metal fullerides came in 1991 when Robert Haddon and Bell Labs announced that K 3C60 had been found to superconduct at 18 K. Larger, non-spherical pure carbon fullerenes that will superconduct have only recently been discovered. In April of 2001, Chinese researchers at Hong Kong University found 1-dimensional superconductivity in single-walled carbon nanotubes at around 15 Kelvin. And in February 2006, Physicists in Japan showed non-aligned, multi-walled carbon nanotubes were superconductive at temperatures as high as 12 K. Silicon-based fullerides like Na 2Ba6Si46 will also superconduct. However, they are structured as infinite networks, rather than discrete molecules. Fullerenes are technically part of a larger l arger family of organic conductors which are described below. superconductors are part of the organic conductor family which includes: molecular salts, polymers and pure carbon systems (including carbon nanotubes and C 60 compounds). The molecular salts within this family are large organic molecules that exhibit superconductive properties at very low temperatures. For this reason they are often referred to as "molecular" superconductors. Their existence was theorized in 1964 by Bill Little of Stanford University. But the first organic (TMTSF)2PF6 The first organic superconductor (TMTSF)2PF6 was not actually synthesized until superconductor discovered. 1980 by Danish researcher Klaus Bechgaard of the University of  Copenhagen and French team members D. Jerome, A. Mazaud, and M. Ribault. About 50 organic superconductors have since been found with Tc's extending from 0.4 K to near 12 K (at ambient pressure). Since these Tc's are in the range of Type 1 superconductors, engineers have yet to find a practical application for them. However, their rather unusual properties have made them the focus of intense research. These properties include giant magnetoresistance, rapid oscillations, quantum hall effect, and more (similar to the behavior of InAs and InSb). In early 1997, it was, in fact (TMTSF)2PF6 that a research team at SUNY discovered could resist "quenching" up to a magnetic field strength of 6 tesla. Ordinarily, magnetic fields a fraction as strong will completely kill superconductivity superconductivity in a material. "Organic"

Organic superconductors are composed of an electron donor (the planar organic molecule) and an electron acceptor (a non-organic anion). Below are a few more examples of organic superconductors. Page 13 of 31

(TMTSF)2ClO4 [tetramethyltetraselenafulvalene [tetramethyltetraselenafulvalene + acceptor] (BETS)2GaCl4 [bis(ethylenedithio)tetraselenafulvalene [bis(ethylenedithio)tetraselenafulvalene + acceptor] (BEDO-TTF)2ReO4H2O [bis(ethylenedioxy)tetrathiafulvalene [bis(ethylenedioxy)tetrathiafulvalene + acceptor] Discovered in 1993 by Bob Cava (currently at Princeton University) and Bell Labs, "Borocarbides" are one of the least-understood superconductor systems of all. It has always been assumed that superconductors cannot be formed from ferromagnetic transition metals - like iron, cobalt or nickel. It's the equivalent of trying to mix oil and water. However, in some borocarbides there is a "soap" that acts to bring these adversaries together. The crystallographic sites for the magnetic ions are thought to be isolated from the conduction path. This allows the cooper pairs to detour around the magnetic ions. Further, when combined with an element that has unusual magnetic properties - like holmium - "reentrant" behavior can also be in evidence in some borocarbides. Below Tc, where it should remain superconductive, there is a discordant temperature at which the material retreats to a "normal", non-superconductive state (see above graphic). To date only one superconductor has been found that has zero resistance at a single temperature - the opposite of reentrant superconductivity. Click HERE to read more about this "resonant" superconductor. Not only the borocarbides recede from a superconductive state at extreme low temperatures. In the compounds HoMo 6S8 (Chevrel) and ErRh4B4 superconductivity suddenly disappears at around 1K. Click here to read more about this phenomenon. As can be seen from some of the below examples, the first metal site in the molecule is always occupied by a rare earth atom. YPd2B2C LuNi2B2C YNi2B2C TmNi2B2C ErNi2B2C HoNi2B2C

23.0 K 16.6 K 15.5 K 11.0 K (resistance increases below Tc) 10.5 K (ferromagnetic) 07.5 K (see above graphic)

NOTE: Other elements that exhibit ferromagnetism have been - by one means or another integrated into superconducting compounds. See the below section on Heavy Fermions. The "Heavy Fermions" sound like a family of overweight circus performers. But, they are yet another example of atypical superconductors. Heavy fermions are compounds containing rare-earth elements such as Ce or Yb, or actinide elements such as U. Their (inner shell) conduction electrons often have effective masses (known as Flux lattices in UPt3 Courtesy Bell Labs

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quasiparticle masses) masses) several hundred times as great as that of "normal" electrons, resulting in what's known as low "Fermi energy" (Ef). This makes them reluctant superconductors. Yet, at cryogenic temperatures, many of these materials are magnetically ordered, others show strong paramagnetic behavior, and some display superconductivity through a mechanism that quickly runs afoul of BCS theory. Research suggests cooper-pairing in the heavy fermion systems arises from the magnetic interactions of the electron spins (D-wave, P-wave, S-wave), rather than by lattice vibrations. The first observation of superconductivity in a heavy fermion system was made by E. Bucher, et al, in 1973 in the compound UBe 13; but, at the time was attributed to precipitated uranium filaments. Superconductivity was not actually recognized, per se, in a heavy fermion compound until 1979 when Dr. Frank Steglich of the Max Planck Institute for Chemical Physics in Solids (Dresden, Germany) realized it was a bulk property in CeCu 2Si2. Heavy fermion superconductivity superconductivity has since been observed in over 20 Ce compounds. In April 2003 a heavy-fermion compound unambiguously exhibited the so-called "FFLO" state, where magnetism and superconductivity have a beneficial coexistence. The compound CeCoIn5 confirmed a theoretical model first put forth in 1964 by Fulde, Ferrell, Larkin, and Ovchinnikov (FFLO). Below are some heavy fermion compounds that will superconduct, along with their Tc's. As can be seen, their transition temperatures are in the range of Type 1 superconductors, superconductors, which severely limits their use in practical applications. CeCoIn5 UPd2Al3 Pd2SnYb URu2Si2 UNi2Al3 Al3Yb UBe13 CeCo2 CePt3Si UPt3 CeCu2Si2

2.30 K (first confirmed FFLO compound) 2.00 K 1.79 K 1.20 K 1.00 K 0.94 K 0.87 K 0.84 K 0.75 K (first heavy fermion superconductor superconductor without a center of symmetry) 0.48 K (see above graphic) 0.1-0.7 K

Note: UGe2 and URhGe2 exhibit simultaneous ferromagnetism and superconductivity. Read more about this phenomenon in the below section on Ruthenates. In the mid 1990's, it was discovered that copper-oxygen planes are not the only superconducting facilitators within the layered perovskites. In 1994 physicists at IBM Zurich and at Hiroshima University collaborated to study the atomic planes of  ruthenium-oxygen due to their similarity to copper-oxygen planes. planes. Yoshiteru Maeno and colleagues found that the compound Magnetic topography of Sr 2RuO4 Sr2RuO4 exhibited superconductivity at 1.5 K. While this is an extremely cold Tc for a superconduc s uperconducting ting perovskite, it revealed a new area of potential among what are known as "Ruthenates" . Shortly after that SrRuO and SrYRuO 6 were also found to superconduct superconduct at similarly low temperatures. When the crystalline structure of some of these materials is broken apart, its surface becomes increasingly ferromagnetic at low temperatures. This phenomenon flies in the face of  condensed matter theory. So much so, that researchers have characterized them as an analog to superfluid Helium-3. And, when copper is added to the mix, even stranger things happen. In June Page 15 of 31

1999 New Zealand researcher Dr. Jefferey Tallon and his German colleague Dr. Christian Bernard discovered a ruthenium-cuprate** whose bulk is both a superconductor and a magnet. Although it was not the first compound discovered that exhibits coexisting ferromagnetism and superconductivity, it's remarkably high Tc of 58 K makes it truly distinct in the world of  superconductors. Unlike "normal" superconductors, this compound becomes diamagnetic at about one-half  Tc. [**RuSr2(Gd,Eu,Sm)Cu2O8 or any parenthetical element partially substituted by Y.] There are many phase transitions that matter goes through on its way to another state (e.g. ice changing to water requires a sudden increase in heat energy). Among the superconductors this is also the case at Tc, Hc and Jc. However, a superconductor has been discovered that exhibits no measurable change in its specific heat (the Ba0.6K0.4BiO3 amount of energy required to increase its temperature by one degree) Courtesy University of Texas while going through up to 3 different "critical" magnetic fields. Ba0.6K0.4BiO3 seems to be the first material discovered that enters a "fourth order" phase transition (according to Ehrenfest's phase transition classification scheme) - something that has never before been observed in nature. Roy Goodrich of Louisiana State University and Donovan Hall of the National High Magnetic Field Laboratory announced this discovery in May, 1999. Not only is this an amazing anomaly in the field of superconductivity. superconductivity. It suggests that even higher order phases may exist in nature. While no one can predict what future discoveries will be made in the field of  superconductivity, some recent developments in the tungsten-bronze system suggest a new vista may be emerging. In July of 1999 researchers Y. Tsabba and S. Reich of the Weizmann Institute in Israel reported possible superconductivity near 91 K in the sodium-doped tungsten-bronze Na0.05WO3. This would be the first known HTS that is not  a cuprate. Most tungsten-bronze compounds that are known to superconduct have Tc's below 4K - making this a truly tantalizing find. °

Other categories of materials that theory suggests may produce superconductors are the higher silver fluorides and complex fluorides - known as  fluoroargentates . Fluoroargentates bear a strong similarity to oxocuprates, compounds that currently have the highest transition temperatures of all known superconductors. In October 2003 researchers Wojciech Grochala, Adrian Porch and Peter P. Edwards reported sudden drops in magnetic susceptibility within a large number of samples of Be-Ag-F. They attribute this to possible spherical regions of superconductivity – with a Tc up to 64 K - couched inside a ferromagnetic host. °

With few exceptions (e.g. polysulphur-nitrides), most polymers resist being coaxed into a superconductive superconductive state. However, some organic polymers exhibit electrical resistance many orders of  magnitude lower than the best metallic conductors. And, they do this at room temperature! These ultraconductors ™, materials such as oxidized atactic polypropylene (OAPP), do not have  zero resistance. But, their enhanced conductivity at ambient temperatures and pressures may actually allow them to compete with superconductors in certain fields. Polypropylene, for example, is normally an insulator. In 1985, however, researchers at the Russian Academy of Sciences discovered that as an oxidized thin-film, polypropylene can have a conductivity 10 5 to 106 higher than the best refined metals. The Meissner effect - the classic criterion for superconductivity cannot be observed, as the critical transition temperature appears to be above the point at which the polymer breaks down (>700K). However, strong (giant) diamagnetism has been confirmed

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TYPE 1 SUPERCONDUCTORS: SUPERCONDUCTORS:  AND A PERIODIC CHART COMPARISON 

T  he Type 1 category of superconductors is

mainly comprised of metals and metalloids that show some conductivity at room temperature. They require incredible cold to slow down molecular vibrations sufficiently to facilitate unimpeded electron flow in accordance with what is known as BCS theory. BCS theory suggests that electrons team up in "Cooper pairs" in order to help each other overcome molecular obstacles - much like race cars on a track drafting each other in order to go faster. Scientists call this process phononmediated coupling because of the sound packets generated by the flexing of o f the crystal lattice. - characterized as the "soft" superconductors superconductors - were discovered first and require the coldest temperatures to become superconductive. They exhibit a very sharp transition to a superconducting state (see above graph) and "perfect" diamagnetism - the ability to repel a magnetic field completely. Below is a list of known Type 1 superconductors along with the critical transition temperature (known as Tc) below which each superconducts. The 3rd column gives the lattice structure of the solid that produced the noted Tc. Surprisingly, copper, silver and Type 1 superconductors

gold, three of the best metallic conductors, do not rank among the superconductive elements.

Lead (Pb) Lanthanum (La) Tantalum (Ta) Mercury (Hg) Tin (Sn) Indium (In) Palladium (Pd)* Chromium (Cr)* Thallium (Tl) Rhenium (Re) Protactinium (Pa) Thorium (Th) Aluminum (Al) Gallium (Ga) Molybdenum Molybdenum (Mo) Zinc (Zn) Osmium (Os) Zirconium (Zr) Americium (Am) Cadmium (Cd) Ruthenium (Ru) Titanium (Ti) Uranium (U)

7.196 K 4.88 K 4.47 K 4.15 K 3.72 K 3.41 K 3.3 K 3K 2.38 K 1.697 K 1.40 K 1.38 K 1.175 K 1.083 K 0.915 K 0.85 K 0.66 K 0.61 K 0.60 K 0.517 K 0.49 K 0.40 K 0.20 K

FCC HEX BCC RHL TET TET (see note 1) (see note 1) HEX HEX TET FCC FCC ORC BCC HEX HEX HEX HEX HEX HEX HEX ORC Page 17 of 31

Hafnium (Hf) Iridium (Ir) Beryllium (Be) Tungsten (W) Platinum (Pt)* Lithium (Li) Rhodium (Rh)

0.128 K 0.1125 K 0.023 K (SRM 768) 0.0154 K 0.0019 K 0.0004 K 0.000325 K

HEX FCC HEX BCC (see note 1) BCC FCC

*Note 1: Tc's given are for bulk (alpha form), except for Palladium, which has been irradiated with. +  He ions, Chromium as a thin film, and Platinum as a compacted powder.

Many additional elements can be coaxed into a superconductive state with the application of  high pressure. For example, phosphorus appears to be the Type 1 element with the highest Tc. But, it requires compression pressures of 2.5 Mbar to reach a Tc of 14-22 K. The above list is for elements at normal (ambient) atmospheric pressure. See the periodic table below for all known elemental superconductors (including Niobium, Technetium and Vanadium which are technically Type 2).

**Note 2: Normally bulk carbon (amorphous, diamond, graphite, white) will not superconduct at  any temperature. However, a Tc of 15K has been reported for elemental carbon when the atoms are configured as highly-aligned, single-walled nanotubes. And non-aligned, multi-walled nanotubes have shown superconductivity near 12K. Since the penetration depth is much larger than the coherence length, nanotubes would be characterized as "Type 2" superconductors.

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TYPE 2 SUPERCONDUCTO SUPERCONDUCTORS: RS:

Except for the elements vanadium, technetium and niobium, the Type 2 category of superconductors is comprised of metallic compounds and alloys. The recently-discovered superconducting "perovskites" (metal-oxide ceramics that normally have a ratio of 2 metal atoms to every 3 oxygen atoms) belong to this Type 2 group. They achieve higher Tc's than Type 1 superconductors by a mechanism that is still not completely understood. Conventional wisdom holds that it relates to the planar layering within the crystalline structure (see above graphic). Although, other recent research suggests the holes of hypocharged oxygen in the charge A Type 2 Layered Cuprate reservoirs are responsible. (Holes are positively-charged vacancies within the lattice.) The superconducting cuprates (copper-oxides) have achieved astonishingly high Tc's when you consider that by 1985 known Tc's had only reached 23 Kelvin. To date, the highest Tc attained at ambient pressure for a material that will form stoichiometrically (by formula) has been 138 K. And the highest Tc overall is 254 K for a material which does not form stoichiometrically (see below list). One theory predicts an upper limit for the layered cuprates (Vladimir Kresin, Phys. Reports 288, 347 - 1997). Others assert there is no limit . Either way, it is almost certain that other, more-synergistic compounds still await discovery among the hightemperature superconductors. °

The first superconducting Type 2 compound, an alloy of lead and bismuth, was fabricated in 1930 by W. de Haas and J. Voogd. But, was not recognized as such until later, after the Meissner effect had been discovered. This new category of superconductors was identified by L.V. Shubnikov at the Kharkov Institute of Science and Technology in the Ukraine in 1936 (1) when he found two distinct critical magnetic fields (known as H c1 and Hc2) in PbTl2. The first of the oxide superconductors was created in 1973 by DuPont researcher Art Sleight when Ba(Pb,Bi)O 3 was found to have a Tc of 13K. The superconducting oxocuprates followed in 1986. Type 2 superconductors - also known as the "hard" superconductors - differ from Type 1 in that their transition from a normal to a superconducting state is gradual across a region of "mixed state" behavior. Since a Type 2 will allow some penetration by an external magnetic field into its surface, this creates some rather novel mesoscopic phenomena like superconducting "stripes" and "flux-lattice vortices". While there are far too many to list in totality, some of the more interesting Type 2 superconductors are listed below by similarity and with descending Tc's. Where available, the lattice structure of the system is also noted. (Tl4Ba)Ba2Ca2Cu7O13+ (As a 9223 structure)

~254 K

(Tl4Ba)Ba4Ca2Cu10Oy (As a 9212/2212C intergrowth.)

~242 K

Tl5Ba4Ca2Cu10Oy (As a 9212/2212C intergrowth.)

~233 K

(Sn5In)Ba4Ca2Cu11Oy (As a B212/2212C intergrowth.)

~218 K

(Sn5In)Ba4Ca2Cu10Oy (As a B212/1212C intergrowth.)

~212 K Page 19 of 31

Sn6Ba4Ca2Cu10Oy (As a B212/1212C intergrowth.)

~200 K

(Sn1.0Pb0.5In0.5)Ba4Tm6Cu8O22+ (As a 1256/1212 intergrowth.)

~195 K

(Sn1.0Pb0.5In0.5)Ba4Tm5Cu7O20+ (As a 1245/1212 intergrowth.)

~185 K

(Sn1.0Pb0.5In0.5)Ba4Tm4Cu6O18+ (As a 1234/1212 intergrowth)

~163 K

Sn3Ba4Ca2Cu7Oy (As a 5212/1212C intergrowth.)

~160 K

(Hg0.8Tl0.2)Ba2Ca2Cu3O8.33 (Hg0.8Tl0.2)Ba2Ca2Cu3O8.33

138 K*

HgBa2Ca2Cu3O8

133-135 K

HgBa2Ca3Cu4O10+ HgBa2Ca3Cu4O10 +

125-126 K

HgBa2(Ca1-xSrx)Cu2O6+ HgBa2(Ca1-xSrx)Cu2O6+

123-125 K

HgBa2CuO4+

94-98 K

Lattice: TET * Note: As a result of a topological "defect", Hg will also go into the Cu atomic sites. Thus, the volume fraction of the intended structure type is considerably less than 100%.

Tl2Ba2Ca2Cu3O10 (Tl1.6Hg0.4)Ba2Ca2Cu3O10+ TlBa2Ca2Cu3O9+ (TlSn)Ba4TmCaCu4Ox (Tl0.5Pb0.5)Sr2Ca2Cu3O9 Tl2Ba2CaCu2O6 TlBa2Ca3Cu4O11 TlBa2CaCu2O7+ Tl2Ba2CuO6 TlSnBa4Y2Cu4Ox Lattice: TET Sn2Ba2(Tm0.5Ca0.5)Cu3O8+ Sn4Ba4(Tm Ca)Cu O SnInBa 4Tm23Cu5Ox7 x

127-128 K 126 K 123 K ~121 K

118-120 K 118 K 112 K 103 K 95 K 86 K

~115 K (Superconductors.ORG - 2005) ~127 structure only) ~113 K K (TmTm-Ca (Superconductors.ORG - 2005)

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Sn3Ba4Tm3Cu6Ox Sn3Ba8Ca4Cu11Ox SnBa4Y2Cu5Ox Sn4Ba4Tm2YCu7Ox Sn4Ba4TmCaCu4Ox Sn4Ba4Tm3Cu7Ox Sn2Ba2(Y0.5Tm0.5)Cu3O8+ Sn3Ba4Y2Cu5Ox SnInBa4Tm4Cu6Ox Sn2Ba2(Sr0.5Y0.5)Cu3O8 Sn4Ba4Y3Cu7Ox Bi1.6Pb0.6Sr2Ca2Sb0.1Cu3Oy Bi2Sr2Ca2Cu3O10*** Bi2Sr2CaCu2O9*** Bi2Sr2(Ca0.8Y0.2)Cu2O8 Bi2Sr2CaCu2O8 Lattice: ORTH

109 K (Superconductors.ORG - 2007) 109 K (One-of-a-Kind Resonant - 2006) 107 K (Superconductors.ORG - 2007) ~104 K (First Hi-Tc Reentrant - 2007) ~100 K (Superconductors.ORG - 2007) ~98 K (Superconductors.ORG - 2006) ~96 K (Superconductors.ORG - 2007) ~91 K (Superconductors.ORG - 2006) 87 K (Superconductors.ORG - 2005)

86 K(Aleksandrov, et al - 1989) ~80 K (Superconductors.ORG - 2005)

115 K (thick film on MgO substrate) substrate) 110 K 110 K 95-96K 91-92K

*** Though not always listed as a component, a small amount of Lead (x=.2-.26) is often used with  Bismuth compounds to help facilitate a higher-Tc crystalline phase.

(Ca1-xSrx)CuO2 YSrCa2Cu4O8+ (Ba,Sr)CuO2 BaSr2CaCu4O8+ (La,Sr)CuO2

110 K 101 K

(Superconductors.ORG - 2007)

90 K 90 K

(Superconductors.ORG - 2007)

42 K

*** The above 5 compounds are all "infinite layer".

Pb3Sr4Ca3Cu6Ox Pb3Sr4Ca2Cu5O15+ (Pb1.5Sn1.5)Sr4Ca2Cu5O15+ Pb2Sr2(Ca, Y)Cu3O8 AuBa2Ca3Cu4O11 AuBa2(Y, Ca)Cu2O7 AuBa2Ca2Cu3O9 Lattice: ORTH

106 K (Superconductors.ORG - 2007) 101 K (Superconductors.ORG - 2005) ~95 K (Superconductors.ORG - 2006)

70 K (Cava, et et al - 1989) 99 K

(Kopnin, et al - 2001)

82 K 30 K

Page 21 of 31

YBa3Cu4Ox (9223C structure) (Y0.5Lu0.5)Ba2Cu3O7 (Y0.5Tm0.5)Ba2Cu3O7 Y3Ba5Cu8Ox Y3CaBa4Cu8O18+ (Y0.5Gd0.5)Ba2Cu3O7 Y2CaBa4Cu7O16 Y3Ba4Cu7O16 Y2Ba5Cu7Ox NdBa2Cu3O7 Y2Ba4Cu7O15 GdBa2Cu3O7 YBa2Cu3O7 TmBa2Cu3O7 YbBa2Cu3O7 YSr2Cu3O7

177 K (Superconductors.ORG - 2009) 107 K (Superconductors.ORG - 2005) 105 K (Superconductors.ORG - 2005) 105 K (Superconductors.ORG - 2008) 99 K (Superconductors.ORG - 2010) 97 K (Superconductors.ORG - 2005) 96 K (Superconductors.ORG - 2006) 96 K (Superconductors.ORG - 2005) 96 K (Superconductors.ORG - 2008)

96 K 95 K 94 K 92 K (See above graphic) 90 K 89 K 62 K

Comment: "1-2-3" superconductors actually have the 1212C structure. Thus, the formula for YBCO could be written CuBa 2YCu2O7 .

GaSr2(Ca0.5Tm0.5)Cu2O7 Ga2Sr4Y2CaCu5Ox Ga2Sr4Tm2CaCu5Ox La2Ba2CaCu5O9+ (Sr,Ca)5Cu4O10 GaSr2(Ca, Y)Cu2O7 (In0.3Pb0.7)Sr2(Ca0.8Y0.2)Cu2Ox (La,Sr,Ca)3Cu2O6 La2CaCu2O6+

99 K (Superconductors.ORG - 2006) 85 K (Superconductors.ORG - 2006) 81 K (Superconductors.ORG - 2006)

79 K (Saurashtra Univ., Rajkot, India 2002) 70 K 70 K 60 K 58 K 45 K Page 22 of 31

(Eu,Ce)2(Ba,Eu)2Cu3O10+ (La1.85Sr0.15)CuO4 SrNdCuO**** (La,Ba)2CuO4 (Nd,Sr,Ce)2CuO4 Pb2(Sr,La)2Cu2O6

43 K 40 K 40 K 35-38 K 35 K 32 K

(La1.85Ba.15)CuO4

30 K (First HTS ceramic SC discovered 1986)

**** First ceramic superconductor discovered without a non-superconducting oxide layer. Comment: All of the above are copper perovskites, even though their metal-to-oxygen ratios are not  exactly 2-to-3. The best performers are those compounds that contain one or more of the electronemitters BaO, SrO or CaO, along with a Period 6 heavy metal like Mercury, Thallium, Lead,  Bismuth, or Gold.

GdFeAsO1-x (Ca,Sr,Ba)Fe2As2 LiFeAs

53.5 K (Highest Tc iron-based compound)

38 K 18 K

Comment: The above are members of the newly discovered iron pnictide family.

MgB2 Ba0.6K0.4BiO3 Nb3Ge Nb3Si Nb3Sn Nb3Al V3Si Ta3Pb V3Ga Nb3Ga V3In

39 K (Highest Tc Non-Fullerene Alloy) 30 K (First 4th order phase compound)

23.2 K 19 K 18.1 K 18 K 17.1 K 17 K 16.8 K 14.5 K 13.9 K

 Lattice: A15 Comment: Among the binary alloys, these are some of the best performers; combining Group 5B metals in a ratio of 3-to-1 with 4A or 3A elements.

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PuCoGa5 NbN

18.5 K (First SC transuranic compound)

16.1 K

Comment: After NbTi (below) NbN is the most widely used low-temperature superconductor.

Nb0.6Ti0.4

9.8 K (First superconductive superconductive wire)

MgCNi3

7-8 K (First all-metal perovskite superconductor) 15 K (as highly-aligned, single-walled nanotubes) 9.25 K

C Nb Tc V

7.80 K 5.40 K

 Lattice: C=Fullerene, C=Fullerene, Nb=BCC, Tc=HEX, V=BCC  Comment: These four are the only elemental Type 2 superconductors.

RuSr2(Gd,Eu,Sm)Cu2O8 ErNi2B2C YbPd2Sn UGe2 URhGe2 AuIn3

Tc ~58 K (Ruthenium-oxocuprate) Tc 10.5 K (Nickel-Borocarbide)

Tc ~2.5 K (Heusler compound) Tc ~1K (Heavy fermion) Tc ~1K ( " )

Tc 50 uK

Comment: The above 6 compounds are all rare ferromagnetic superconductors.

Sr.08WO3 Tl.30WO3 Rb.27-.29WO3

2-4 K (Tungsten-bronze)

2.0-2.14 K (") 1.98 K (")

 Lattice: TET  (1.) "History of Physics Research in Ukraine", by Oleksandr Bakai and Yurij Raniuk, Kharkov  Institute of Science and Technology, 1993.

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 APPLICATION OF SUPERCONDUCTORS:

 M  agnetic-levitation is an application

where superconductors perform extremely well. Transport vehicles such as trains can be made to "float" on strong superconducting magnets, virtually eliminating friction between the train and its tracks. Not only would conventional electromagnets waste much of the electrical energy as heat, they The Yamanashi MLX01 Maglev train. would have to be physically much larger than superconducting superconducting magnets. A landmark for the commercial use of MAGLEV technology t echnology occurred in 1990 when it gained the status of a nationally-funded project in Japan. The Minister of Transport authorized construction of the Yamanashi Maglev Test Line which opened on April 3, 1997. In December 2003, the MLX01 test vehicle (shown above) attained an incredible speed of  361 mph (581 kph). Although the technology has now been proven, the wider use of MAGLEV vehicles has been constrained by political and environmental concerns (strong magnetic fields can create a biohazard). The world's first MAGLEV train to be adopted into commercial service, a shuttle in Birmingham, England, shut down in 1997 after operating for 11 years. A Sino-German maglev is currently operating over a 30-km course at Pudong International Airport in Shanghai, China. The U.S. plans to put its first (non-superconducting) Maglev train into operation on a Virginia college campus. Click this link for a website that lists other uses for MAGLEV. An area where superconductors can perform a life-saving function is in the field of biomagnetism. Doctors need a non-invasive means of  determining what's going on inside the human body. By impinging a strong superconductor-derived magnetic field into the body, hydrogen atoms that exist in the body's water and fat molecules are forced to accept energy from the magnetic field. They then release this energy at a frequency that can be detected and displayed graphically by a computer. Magnetic Resonance Imaging (MRI) was actually discovered in the mid 1940's. But, the first MRI of a Human Skull. MRI exam on a human being was not performed until July 3, 1977. And, it took almost five hours to produce one image! Today's faster computers process the data in much less time. The Korean Superconductivity Group within KRISS has carried biomagnetic technology a step further with the development of a double-relaxation oscillation SQUID (Superconducting QUantum Interference Device) for use in Magnetoencephalography. SQUID's are capable of  sensing a change in a magnetic field over a billion times weaker than the force that moves the needle on a compass (compass: 5e-5T, SQUID: e-14T.). With this technology, the body can be probed to certain depths without the need for the strong st rong magnetic fields associated with MRI's. Probably the one event, more than any an y other, that has been responsible for putting "superconductors" into the American lexicon was the Superconducting Super-Collider project   planned for construction in Ellis county, Texas.

Though Congress cancelled the multi-billion dollar effort in 1993, the concept of such a large, highenergy collider would never have been viable

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without superconductors. High-energy particle research hinges on being able to accelerate subatomic particles to nearly the speed of light. Superconductor magnets make this possible. CERN, a consortium of several European nations, is doing something similar with its Large Hadron Collider (LHC) recently inaugurated along the Franco-Swiss border. Electric generators made with superconducting wire are far more efficient than conventional generators wound with copper wire. In fact, their efficiency is above 99% and their size about half  that of conventional generators. These facts make them very lucrative ventures for power utilities. General Electric has estimated the potential worldwide worl dwide market for superconducting generators in the next decade at around $20-30 billion dollars. Late in 2002 GE Power Systems received $12.3 million in funding from the U.S. Department of Energy to move high-temperature superconducting generator technology toward full commercialization. Other commercial power projects in the works that employ superconductor technology include energy storage to enhance power stability. American Superconductor Corp. received an order from Alliant Energy in late March 2000 to install a Distributed Superconducting Magnetic Energy Storage System (D-SMES) in Wisconsin. Just one of these 6 D-SMES units has a power reserve of over 3 million watts, which can be retrieved whenever there is a need to stabilize line voltage during a disturbance in the power grid. AMSC has also installed more than 22 of its D-VAR systems to provide instantaneous reactive power support.

The General Atomics/Intermagnetics General superconducting Fault Current Controller, employing HTS superconductors.

Recently, power utilities have also begun to use superconductor-based transformers and "fault limiters". The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. ABB also recently announced the development of a 6.4MVA (mega-volt-ampere) fault current limiter - the most powerful in the world. This new generation of HTS superconducting fault limiters is being called upon due to their ability to respond in just thousandths of a second to limit tens of thousands of amperes of current. Advanced Ceramics Limited is another of several companies that makes BSCCO type fault limiters. Intermagnetics General recently completed tests on its largest (15kv class) power-utility-size fault limiter at a Southern California Edison (SCE) substation near Norwalk, California. And, both the US and Japan have plans to replace underground copper power cables with superconducting BSCCO cable-in-conduit cooled with liquid nitrogen. (See photo below.) By doing this, more current can be routed through existing cable tunnels. In one instance i nstance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper wire, making it over 7000% more space-efficient. An idealized application for superconductors is to employ them in the transmission of commercial power to cities. However, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short "test runs". In May of 2001 some 150,000 residents of Copenhagen, Denmark, began receiving their Page 26 of 31

electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes. In the summer of 2001 Pirelli completed installation of three 400-foot HTS cables for Detroit Edison at the Frisbie Substation capable of  delivering 100 million watts of power. This marked the first time commercial power has been delivered to customers of a US power utility utilit y through superconducting wire. Intermagnetics General has announced that its IGC-SuperPower subsidiary has joined with BOC and Sumitomo Electric in a $26 million project to install an underground, HTS power cable in Albany, New York, in Niagara Mohawk Power Corporation's power grid. Sumitomo Electric's DI-BSCCO cable was employed in the first in-grid power cable demonstration project sponsored by the U.S. Department of Energy and New York Energy Research & Development Authority. After connecting to the grid successfully on July 2006, the DI-BSCCO cable has been supplying the power to approximately 70,000 households without any problems. The long-term test will be completed in the 2007-2008 timeframe.

Hypres Superconducting Microchip, Incorporating 6000 Josephson Junctions.

The National Science Foundation, along with NASA and DARPA and various universities are currently researching "petaflop" computers. A petaflop is a thousand-trillion floating point operations per second. Today's fastest computers have reached "petaflop" speeds - quadrillions of  operations per second. Currently the fastest is a U.S. Military Supercomputer call the "Road Runner" operating at 1.026 petaflops per second (with multiple CPU's). The fastest single processor is a Lenslet optical DSP running at 8 teraflops. It has been conjectured that devices on the order of  50 nanometers in size along with unconventional switching mechanisms, such as the Josephson  junctions associated with superconductors, will be necessary to achieve the next level of processing speeds. TRW researchers (now Northrop Grumman) have quantified this further by predicting that 100 billion Josephson junctions on 4000 microprocessors will be necessary to reach 32 petabits per second. These Josephson junctions are incorporated into field-effect transistors which then become part of the logic circuits within the processors. Recently it was demonstrated at the Weizmann Institute in Israel that the tiny magnetic fields that penetrate Type 2 superconductors can be used for storing and retrieving digital information. It is, however, not a foregone conclusion that computers of the future will be built around superconducting devices. Competing technologies, such as quantum (DELTT) transistors, high-density molecule-scale processors, and DNA-based processing also have the potential to achieve petaflop benchmarks. In the electronics industry, ultra-high-performance filters are now being built. Since superconducting superconducting wire has near zero resistance, even at high frequencies, many more filter stages can be employed to achive a desired frequency response. This translates into an ability to pass desired frequencies and block undesirable frequencies in high-congestion rf (radio frequency) applications such as cellular telephone systems. ISCO International and Superconductor Technologies are companies currently offering such filters. Superconductors have also found widespread applications in the military. HTSC SQUIDS are being used by the U.S. NAVY to detect mines and submarines. And, significantly smaller motors are being built for NAVY ships using superconducting wire and "tape". In mid-July, 2001, American Superconductor unveiled a 5000-horsepower motor made with superconducting wire Page 27 of 31

(below). An even larger 36.5MW HTS ship propulsion motor was delivered to the U.S. Navy in late l ate 2006. The US Air Force expects planes will be able to fire non-lethal microwave rays at enemy ground troops with the help of a new superconducting generator system. The new generators are about the size of a small beer keg and designed to produce five megawatts of power. The generators will have lightweight metal foils coated with superconducting material that carry many times more current and are more efficient, strong enough for microwave weapons and light enough for airplanes. The newest application for HTS wire is in the degaussing of  naval vessels. American Superconductor has announced the development of a superconducting degaussing cable. Degaussing of a ship's hull eliminates residual magnetic fields which might otherwise give away a ship's presence. In addition to reduced power requirements, HTS degaussing cable offers reduced size and weight. The military is also looking at using superconductive tape as a means of reducing the length of very low frequency antennas employed on submarines. Normally, the lower the frequency, the longer an antenna must be. However, inserting a coil of wire ahead of the antenna will make it function as if it were much longer. Unfortunately, this loading coil also increases system losses by adding the resistance in the coil's wire. Using superconductive materials can significantly reduce losses in this coil. The Electronic Materials and Devices Research Group at University of  Birmingham (UK) is credited with creating the first superconducting microwave antenna. Applications engineers suggest that superconducting carbon nanotubes might be an ideal nanoantenna for high-gigahertz and terahertz frequencies, once a method of achieving zero "on tube" contact resistance is perfected. The most ignominious military use of superconductors may come with the deployment of  "E-bombs". These are devices that make use of strong, superconductor-derived magnetic fields to create a fast, high-intensity electro-magnetic pulse (EMP) to disable an enemy's electronic equipment. Such a device saw its first use in wartime in March 2003 when US Forces attacked an Iraqi broadcast facility.

A photo of Comet 73P/Schwassmann-Wachmann 3, in the act of disintegrating , taken with the European Space Agency S-CAM.

Among emerging technologies are stabilizing momentum wheel (gyroscope) for earthorbiting satellites that employs the "flux-pinning" properties of imperfect superconductors to reduce friction to near zero. Superconducting Superconducting x-ray detectors and ultra-fast, superconducting light detectors are being developed due to their inherent ability to detect extremely weak amounts of energy. Already Scientists at the European Space Agency (ESA) have developed what's being called the SCam, an optical camera of phenomenal sensitivity (see above photo). And, superconductors may Page 28 of 31

even play a role in Internet communications soon. In late February, 2000, Irvine Sensors Corporation received a $1 million contract to research and develop a superconducting digital router for high-speed data communications up to 160 GHz. Since Internet traffic is increasing exponentially, superconductor technology may be called upon to meet this super  need. Irvine Sensors speculates speculates this router r outer may see use in facilitating Internet2. According to June 2002 estimates by the Conectus consortium, the worldwide market for superconductor products is projected to grow to near US $5 billion by the year 2010 and to US $38 billion by 2020. Low-temperature superconductors are expected to continue to play a dominant role in well-established fields such as MRI and scientific research, with hightemperature superconductors enabling the newer industries. The above ISIS graph gives a rough breakdown of the various markets in which superconductors are expected to make a contribution. All of this is, of course, contingent upon a linear growth rate. Should new superconductors with higher transition temperatures be discovered, growth and development in this exciting field could explode virtually overnight. Another impetus to the wider use of superconductors is political in nature. The reduction of  green-house gas (GHG) emissions has becoming a topical issue due to the Kyoto Protocol which requires the European Union (EU) to reduce its emissions by 8% from 1990 levels by 2012. Physicists in Finland have calculated that the EU could reduce carbon dioxide emissions by up to 53 million tons if high-temperature superconductors superconductors were used in power plants. pl ants. The future melding of superconductors into our daily lives li ves will also depend to a great degree on advancements in the field of cryogenic cooling. New, high-efficiency magnetocaloric-effect compounds such as gadolinium-silicon-germanium are expected to enter the marketplace soon. Such materials should make possible compact, refrigeration units to facilitate additional HTS applications.

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SUPERCONDUCTOR LINKS:   Below are various links to web sites dealing with superconductors and/or related fields; some of which may already be listed on the USES, NEWS or PLAY pages.

YBCO Molecule

 Pictures/Graphics/Animations:        

Pictures & Animations of Levitating Magnets | University of Oslo Images of Levitating Objects | The Magnet Man Micro-photographs Micro-photographs of Superconducting Materials | FSU Gallery Magneto-Optical Magneto-Optical Imaging of Superconductors Superconductors | University of Oslo Perovskite Structures | Center for Computational Materials Science Gallery of Abrikosov Lattices in Superconductors | University of Oslo Crystal Atomic Lattice Viewer | University of Leicester Crystal Structures | Israel Institute of Technology

Tutorial/Research:         

Superconductivity Superconductivity In Its Simplest Form | Oxford University Superconductivity Superconductivity Concepts Link Map | Georgia State University Lectures on Superconductivity | University of Cambridge High-Temperature Superconductors Superconductors | Kent State University Condensed Matter Theory | University of Michigan Advanced Explanation of Superconductivity | Futurescience Flux Lines in Type 2 Superconductors | Univ. of California, Santa Barbara Hole Theory of Superconductivity | Univ. of California, San Diego Oxide Superconductors Tutorial | by Bob Cava of Princeton University for the American Ceramic Society

 Reference:             

Physica C | Superconductivity Journal NIST Superconducting Materials Database | National Institute of Standards and Technology Iowa State High-Tc Searchable Database Archive | Iowa State/Ames Lab KEIRIN Superconductivity Papers Database | Japan J apan Solid State Communications | Elsevier Science Superconductor Superconductor Science and Technology | Institute Of Physics Home page for the 1913 Nobel speech by Heike Kamerlingh Onnes Home page for the 1972 Nobel speeches | by John Bardeen, Leon Cooper, and John Schreiffer Home page for the 1973 Nobel speech by Brian D. Josephsen J osephsen Home page for the 2003 Nobel speeches to Abrikosov, Ginzburg and Leggett U.S., European and Japanese Patent Search | Refined Search High School Teacher's Guide to Superconductivity | Oak Ridge National Laboratory Books on Superconductivity | Geometry.NET Picks Page 30 of 31

   

Books on Superconductivity | RBookShop Picks Glossary of Superconductor Terms | Superconductors.ORG Matter Glossary | University of Liverpool Ionic Radii of the Elements | Environmentalchemistry.COM

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