The Heat is On... and Measured

Evaluating how temperature affects superconductor performance has become far more precise -- thanks to a recent development by Weizmann Institute Scientists.

Unique in their capacity to conduct electricity without resistance, superconductors may serve to transport electric currents across vast distances and can be used in a variety of industrial and transportation technologies. A considerable number of these innovations are based on the ability to manipulate the way in which superconductors are penetrated by magnetic fields.

The fields infiltrate some of the superconductors in the form of tiny whirlpools, or vortices, each containing a weak magnetic flux at its core. These whirlpools should usually settle at equal distances from each other, in a fashion similar to the arrangement of molecules within a solid crystal. However, Prof. Eli Zeldov of the Weizmann Institute's Department of Condensed Matter Physics has previously proven that under certain conditions this solid 'crystal' may undergo a 'meltdown' so that the whirlpools are transformed to a disorganized state resembling the material's liquid structure.

In the present study, due to appear in the July 20 issue of Nature, Zeldov, doctoral student Alexander Soibel, and research associates Yuri Myasoedov and Michael Rappaport succeeded in visualizing the transition of these magnetic whirlpools from their solid to liquid state and back again, when exposed to temperature variations. To do so, they built a unique optical microscope measuring system based on directing a polarized light at an optical gauge on the superconductor surface, and measuring the resultant change in polarized light reflected back from the sample.

The system, which is more than one hundred times more sensitive than previous methods, reveals how temperature changes cause the whirlpool solid to melt or alternatively form complex solid-liquid patterns. By taking sequential images, the Weizmann scientists were able to create a 'movie' capturing the nucleation and propagation of the melting and freezing processes. These recordings should further the understanding of how temperature changes affect superconductor performance, including the influence of material defects within the superconductor.

This research was funded by the Philip Klutznick Endowed Scientific Research Fund and the Robert and Giampiero Alhadeff Research Award. Prof. Eli Zeldov holds the David and Inez Myers Chair of Condensed Matter Physics.

The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel. Its 2,500 scientists, students and support staff are engaged in more than 1,000 research projects across the spectrum of contemporary science.