Many superconductors are rendered almost useless by the motion of string-like magnetic vortices. But because these vortices are hard to cut, it may be possible to pin them down using some very old techniques. Many properties of materials depend crucially on defects. Soft metals bend irreversibly when dilute concentrations of defects called dislocation lines move in response to an applied stress. The Bronze Age began when early metallurgists added small concentrations of tin to copper to create a stronger and more effective material — the impurities work by pinning dislocations in place, thus preventing plastic deformation.
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