With electricity such a familiar part of our lives, measuring the electric current that flows through a material sounds fairly old hat. Yet Weizmann Institute scientists have made a surprising new discovery related to the behavior of electric currents in materials known as superconductors, whose resistance to the flow of electricity is exceedingly low.
Dan Fuchs and Prof. Eli Zeldov of Weizmann's Condensed Matter Physics Department, along with their colleagues, revealed that electric current doesn't always flow across a superconductor uniformly, as was previously believed. Rather, when the temperature is relatively high, the current flows almost exclusively at both edges of the superconductor sample. In a way, the current behaves much like bowling balls that veer from center and slip into the gutter, a trough that channels them quickly to the end of the lane. This is in contrast to the behavior of electric current in normal metals, through which the flow of electricity is evenly dispersed. This study was recently reported in Nature (Jan. 22, 1998) and will be further described in June in Physical Review Letters.
Superconductors fascinate scientists both because of the basic research questions and because these materials may one day be used in many areas, from building levitating trains to manufacturing superfast computers.
In superconductors, resistance to electric current is created by a dynamic magnetic field within the material. The field, which takes the form of numerous long spaghetti-like tubes or columns, is in constant motion and interferes with the flow of the current, causing it to dissipate. Weizmann Institute scientists used unique microscopic sensors that make it possible to map the distribution and movement of these columns with unprecedented precision. They found that at relatively high temperatures -- ranging from 35 to 70 K -- a phenomenon known as the "surface barrier" causes the columns at the edges of the superconductor to slow down. It is this slowing-down that creates a path of low resistance, "inviting" the electric current to flow along the edge rather than through the bulk of the material.
The Institute discovery throws a radically new light on the properties of superconductors and may help scientists produce superconductor materials with advanced properties.
The team led by Prof. Zeldov included Dr. Michael Rappaport and Dr. Hadas Shtrikman of the Weizmann Institute and Prof. Tsuyoshi Tamegai and Shuuichi Ooi of the University of Tokyo. This work was supported by the Israel Science Foundation, the German-Israeli Foundation for Scientific Research and Development (GIF), the Minerva Foundation, the Alhadeff Research Award and Japan's Ministry of Education, Science, Sports and Culture.
The Weizmann Institute of Science, in Rehovot, Israel, is one of the world's foremost centers of scientific research and graduate study. Its 2,500 scientists, students, technicians, and engineers pursue basic research in the quest for knowledge and the enhancement of the human condition. New ways of fighting disease and hunger, protecting the environment, and harnessing alternative sources of energy are high priorities.
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