Unexpected boost: a superconductivity killer's silver lining. (This Week).A bad neighbor sometimes has a good influence on the folks next door. Superconductivity superconductivity, abnormally high electrical conductivity of certain substances. The phenomenon was discovered in 1911 by Kamerlingh Onnes, who found that the resistance of mercury dropped suddenly to zero at a temperature of about 4.2°K;. researchers are discovering their own version of this experience. Physicists have long been wary of ordinary metals that, when they share physical borders with superconductors, sap their neighbors of their no-resistance conductivity. This phenomenon is known as the proximity effect Proximity effect may refer to:
An ordinary metal that's next door to one particular class of superconductors--those with so-called strongly correlated systems of electrons--can actually boost the neighboring material's superconductivity. Among the superconductors that fall into this class are high-temperature superconductors (SN: 3/16/02, p. 173). They superconduct in much warmer--though still bitterly cold--conditions than ordinary superconductors do. Physicists have long sought ways of coaxing high-temperature superconductors to function at even higher temperatures (SN: 12/2/00, p. 359). The newfound "inverse proximity effect" may offer an avenue toward that goal, says Robert C. Dynes Dr. Robert C. Dynes (born November 8, 1942 in London, Ontario, Canada), Ph.D, is the president of the University of California system. He is also a professor of physics at the University of California, Berkeley. of the University of California, San Diego UCSD is consistently ranked among the top ten public universities for undergraduate education in the United States by U.S. News & World Report.[3] It is a Public Ivy. [1] For graduate studies, most of UCSD's Ph.D. , leader of the new study. Also, since magnetic field sensors, extremely powerful magnets, and many of the other superconducting devices Superconducting devices Devices that perform functions in the superconducting state that would be difficult or impossible to perform at room temperature, or that contain components which perform such functions. exploit the ordinary proximity effect, the inverse effect will probably lead to novel devices, he predicts. Dynes and his colleagues have "discovered an anomaly in the proximity effect that challenges our understanding of superconductivity," comments Robert J. Soulen of the Naval Research Laboratory Noun 1. Naval Research Laboratory - the United States Navy's defense laboratory that conducts basic and applied research for the Navy in a variety of scientific and technical disciplines NRL (NRL Noun 1. NRL - the United States Navy's defense laboratory that conducts basic and applied research for the Navy in a variety of scientific and technical disciplines Naval Research Laboratory ) in Washington, D.C. He and Michael S. Osofsky, also of NRL, have developed a theoretical model to predict how structures of superconducting materials affect the so-called critical temperatures at which superconductivity kicks in. When the scientists plugged the new inverse-effect data into their model last week, "it fit like a glove," Soulen says. Dynes and his collaborators began their work on a hunch that there is an inverse proximity effect. However, because high-temperature superconductors are such complex materials, the team chose to start with simpler ingredients. It zeroed in on lead, an ordinary superconductor A material that has little resistance to the flow of electricity. Traditional superconductors operate at absolute zero (-459.67 degrees Fahrenheit or -273.15 degrees Celsius). Experiments in the 1980s raised the temperature to -321 degrees Fahrenheit. . However, they knew it would become a strongly correlated system if they fabricated it in extremely thin layers--only several atoms thick--in which the atoms assumed a disorderly, noncrystalline atomic arrangement. The researchers then deposited silver on lead films to serve as the neighboring metal. The team found that the temperatures at which the lead layers became superconducting increased ever so slightly as the silver overlayer increased to a thickness of 0.26 nanometer. That minute change in critical temperature--from about 1.6 Kelvins to just over 1.8 K--signified that the lead film had become a better superconductor. When the layers of either metal became too thick, the conventional proximity effect took over, and the lead's critical temperature declined. Measurements indicating the amount of energy needed to break up the electronic pairings that underlie superconductivity--another gauge of how effectively a film superconducts--also showed a telltale rise and fall that indicates an inverse proximity effect. Dynes, Olivier S. Bourgeois, now of the National Center for Scientific Research in Grenoble, France, and Aviad Frydman of Bar Ilan University in Ramat Gan Ramat Gan (rä`mät gän), city (1994 pop. 122,200), W central Israel, adjacent to Tel Aviv. Founded in 1921, Ramat Gan is an important industrial center. Food processing is the chief industry; construction materials are also made there. , Israel, report their findings in the May 6 Physical Review Letters Physical Review Letters is one of the most prestigious journals in physics.[1] Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. . |
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