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Smallest Superconductors

Scientists at Freie Universität Berlin Have Shown How Small Magnets Disrupt the Flow of Electricity without Resistance

№ 149/2011 from May 20, 2011

Scientists at Freie Universität Berlin have demonstrated the local disturbance of superconductors by small magnets. They created a complex interaction, which has been discussed in theory for decades, but until now could not be proven experimentally. Superconductivity describes a state in which current can flow without resistance. Prof. Dr. Katharina Franke, Dr. Gunnar Schulze, and Prof. Dr. Jose Ignacio Pascual at the Department of Physics published their proof of the local disturbance of superconductivity by small magnets in Science.

Superconductors are particularly important for technological applications. Superconducting coils to generate magnetic fields are used, for example, in MRI scanners or particle accelerators. However, if the generated magnetic field is too large, the superconducting state collapses. Currently this is circumvented using special superconducting materials, so-called type-II superconductors. The reasons for the destruction of superconductivity in the conventional type-I superconductors have not been adequately researched.

The smallest possible magnets are single atoms or molecules. In their experiments the researchers examined how individual magnetic molecules on a superconducting lead surface change the conductivity in their immediate surroundings. The particles that make up the superconductivity are pairs of electrons known as Cooper pairs. They can move without resistance through the crystal. In the vicinity of magnetic molecules, however, a force acts on them, so they become unstable until they finally break up completely. This could be demonstrated by conductivity. In addition, the research team was able to show how the "normal" electrons that are also in the superconductor respond to the magnetic molecules. The scientists believe these investigations have created an improved understanding of the fundamentals for new technological applications.

Published in: Science 332, 940 (2011)

Online: www.sciencemag.org/content/332/6032/940.full.pdf

For further information, please contact:

Prof. Dr. Katharina Franke, Department of Physics, Freie Universität Berlin
Tel.: +49 (0)30 / 838-56149; Email: franke@physik.fu-berlin.de