Number 28 (Story #1), April 4, 1991 by Phillip F. Schewe and Ben Stein|
SCREW DISLOCATIONS IN SUPERCONDUCTING FILMS have shown up in scanning tunneling microscope images made by J. Georg Bednorz's group at IBM-Zurich. The spiral structures, which form when the Y-B-Cu-O films are grown epitaxially, may be one reason why the pinning of magnetic flux lines (and hence the critical current density) is better in thin-film high-temperature superconductors than in bulk versions (Nature, Mar. 28, 1991). Ian Raistrick and a group of scientists at Los Alamos have also observed the spiral grains; they found that the grains were rectangular in shape if grown on magnesium oxide and more circular if grown on strontium titanate. (Science, Mar. 29, 1991). Both groups previously reported their results on March 18 at the APS March Meeting in Cincinnati.