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To: Real Man who wrote (101686)	5/11/2001 8:59:13 PM
From: yard_man	Respond to of 436258

Do you work for Bell Labs? -- get last month's copy of IEEE Spectrum OK it wasn't high temp, but I think I have heard something about folks workign on them >>First Plastic Superconductor Is Identified Aresearch team from the United States, Germany, and Switzerland has demonstrated the first organic polymer superconductor--a thin film of conducting polythiophene that loses all electric resistance below 2.35 K. The invention of polymers that conduct electricity was recognized by the Nobel Prize for Physics last year [IEEE Spectrum, December, p. 18]. Now several research groups are investigating how the materials can be used to create transistors, light-emitting diodes, and flat-panel computer displays. In such polymers, surplus charge-carriers hop from one molecule to the next, being supplied either by the introduction of impurities (or dopants) or by injection from an external source. Previous failures to create a superconducting polymer were due to the use of chemical dopants, which scatter the charge-carriers and so make a superconducting current hard to achieve, explained team member Zhenan Bao, a chemist at Bell Laboratories in Murray Hill, N.J. Instead, the researchers opted to use an experimental setup based on a field-effect transistor (FET). A gate electrode deposited on a glass substrate is separated by a thin aluminum oxide layer from a thin polythiophene film. The resistance in the film is measured via the two inner contacts [diagram]. A voltage of up to 200 V applied to the gate attracts electrons from the bulk of the polymer and concentrates them into a layer, only a few molecules thick, adjacent to the aluminum oxide insulator, where the current flows. The team reported in the 8 March issue of Nature that the layer's electric resistance dropped to zero at temperatures below 2.35 K, but lost its superconducting properties upon the application of a magnetic field--another sure sign that one is dealing with a superconductor, said Bao. Just as with ceramic high-temperature superconductors, achieving superconduction in a polymer was a matter of trial and error. "We had to make an educated guess about what might and might not work," said team member Bertram Batlogg of the Federal Institute of Technology in Zürich, Switzerland. According to Denis Jérome, of the University of Paris at Orsay, the result is also an experimental triumph because the polymer created by the team had a highly well-ordered crystalline structure. That feat will boost the technology of polymer electronics in general. "They have a much 'cleaner' system as compared to the doped polymers....They can master the technology of the organic transistor," said Jérome. The researchers believe that the superconducting mechanism in the polymer is akin to that in superconducting metals. Besides being intrinsically exciting, a plastic superconductor could have important applications because of its malleability and manufacturability. <<

To: Real Man who wrote (101686)	5/11/2001 9:06:09 PM
From: yard_man	Respond to of 436258

Here's a related story on Magnesium Diboride >>SUPERCONDUCTIVITY Unsuspected Superconductor Wows Physicists, Technologists A simple, commonly available metallic compound, magnesium diboride, could be ideal for wires and magnets An inexpensive metallic compound has been found to be a remarkable superconductor, to the great excitement of physicists, who predict it could not only produce sharper images in magnetic resonance imaging (MRI) machines, but also improve efficiency in power plants. The compound, magnesium diboride, is a common reagent in chemistry laboratories, but until recently had never been tested for superconductivity--an absence of resistance to the flow of electricity in a material cooled below a certain critical temperature. Earlier this year, five Japanese physicists announced that they had accidentally discovered that the diboride is a superconductor below 39 K (389 °F). Cold as this sounds, it is much higher than temperatures at which other known metallic compounds exhibit superconductivity. The higher the critical temperature of a superconductor, the easier it is to use commercially. -------------------------------------------------------------------------------- A 100-gram bottle of magnesium diboride costs about $200 -------------------------------------------------------------------------------- The findings of the researchers in Japan, led by Professor Jun Akimitsu of Tokyo's Aoyama-Gakuin University, saw print in the 1 March issue of the journal Nature, although they had been reported earlier at a conference in January. "I discovered a sign of superconductivity in August last year," Akimitsu told IEEE Spectrum, outlining the chronology of events. While trying to use magnesium diboride to make calcium hexaboride, a material with unusual physical properties, the team stumbled on the fact that the former was a superconductor. "I talked about it on 10 January this year at a small meeting at Sendai," he added. The news immediately spread over the world's e-mail networks, setting off a race to investigate magnesium diboride's potential. Groups in the United States promptly confirmed the Japanese results. "From a technological standpoint, this material is extremely exciting," said Steven Simon, the director of theoretical physics at Lucent Technologies Inc.'s Bell Laboratories, Murray Hill, N.J. "This material may very well make the world's best superconducting wires and superconducting magnets." One promising application could be in magnetic resonance imaging (MRI) machines, which rely on superconducting magnets. And if wires can be made out of magnesium diboride, they could be used to transmit power, observed Robert J. Cava, a professor of chemistry at Princeton University, New Jersey. A team of physicists led by Paul Canfield of Iowa State University has already succeeded in creating small wires out of magnesium diboride by passing magnesium vapors over boron fibers. But the wires are only about 5 cm long and are unsuitable for industrial applications. Since magnesium diboride is somewhat brittle, it will be a challenge to make wires that are longer and bendable. Still, physicists are optimistic. Good vibrations Another reason physicists are fascinated by magnesium diboride is that preliminary data suggest that it is a conventional superconductor--a material that can be explained by the Bardeen-Cooper-Schrieffer (BCS) mechanism of superconductivity. The BCS theory states that the thermal vibrations of atoms in the crystal structure of the material govern the interactions between the electrons in a superconductor. In contrast, the high-temperature superconductors, operating at temperatures attainable with liquid-nitrogen cooing, are poorly understood. Although they have higher critical temperatures than magnesium diboride, they are difficult to work with and very expensive. A 100-gram bottle of magnesium diboride is relatively inexpensive. "The most important implications [of the recent discovery] are the applications," Akimitsu said. "This material has many characteristic features--it's very light, cheap, and easily made." What's next? The Japanese group is looking for similar superconductors with higher critical temperatures, said Akimitsu. In labs around the world, physicists have joined the search. "If I didn't know better, I'd think we'd all been dreaming for the past few weeks," wrote Cava in Nature. "How much this discovery changes the path of materials physics depends on whether magnesium diboride is a solitary example of making high-temperature superconductors or whether it represents only the tip of an iceberg." <<