Electrical superball pulls itself together.A strong electric field can drive tiny particles of a 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. to bind themselves together into a remarkably sturdy ball about 0.25 millimeter across. Rongjia Tao of Southern Illinois University Southern Illinois University, main campus at Carbondale; state supported; coeducational; est. 1869, opened 1874 as a normal school, renamed 1947. It has a center for archaeological investigation and a fisheries research laboratory. There is also a campus at Edwardsville. at Carbondale and his collaborators report this surprising phenomenon in the Dec. 27, 1999 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. . Their finding "reveals a new property of high-temperature superconductivity Unsolved problems in physics: What is the responsible mechanism that causes certain materials to exhibit superconductivity at temperatures much higher than around 50 kelvin? High-temperature superconductors (abbreviated high ," the researchers remark. Tao and his coworkers were initially interested in observing the motion of superconducting particles, a few micrometers in diameter, in an electric field. The researchers examined particles composed of a copper oxide Noun 1. copper oxide - an oxide of copper oxide - any compound of oxygen with another element or a radical compound that loses its resistance to the flow of electric current below a certain temperature. They suspended these grains in liquid nitrogen Noun 1. liquid nitrogen - nitrogen in a liquid state atomic number 7, N, nitrogen - a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living at 77 kelvins, which is below the threshold. The researchers expected the widely dispersed particles to behave in one of two ways. The grains might bounce between the two electrodes that created the guiding electric field like bits of ordinary metals, such as copper, iron, and aluminum. Or they might act as ceramic material and form strings aligned with the field. Instead, several million particles rapidly packed themselves into a roughly spherical ball. The sphere was robust enough to move as a single, electrically charged entity and survive repeated collisions with the electrodes. Sometimes, two or more balls would form. "There were no previous indications that aggregation of superconducting particles would occur," says physicist N. Phuan Ong of Princeton University. The force binding the ball together seems to be an artifact of 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;. . The superconducting bali's spherical shape indicates that a new type of surface tension related to superconductivity comes into play, says Princeton theorist Philip W. Anderson. Researchers may be able to take advantage of this surface tension to lay down thin superconducting films on solid surfaces, Tao says. He and his team are now investigating possible applications of such films. |
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