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Researchers Find Magnetic Link to High-temperature Superconductivity
Word of the Week: Meissner Effect
Friday - February 18, 2011 |
Researchers Find Magnetic Link to High-temperature SuperconductivityResearchers from the Stanford Institute for Materials and Energy Science, a joint SLAC-Stanford institute, have seen strong indications of a relationship between the superconductive and magnetic properties of high-temperature superconductors—a relationship long suspected but difficult to investigate experimentally. Any step toward a real understanding of high temperature superconductors is a big step right now. Today's superconductors need extreme cold to keep conducting electricity with 100 percent efficiency, but extreme cold is not cheap. If current research leads to room temperature superconductors, superconducting technologies such as loss-less power lines and levitating high-speed trains will be economically as well as technically feasible. A paper in last week's Physical Review Letters explains how the researchers, led by Kathryn Moler, attacked the mystery by employing a new technique to investigate a suspected connection between magnetism and superconductivity in high-temperature superconductors called iron pnictides. The researchers "doped" the pnictide crystals (in this case barium iron arsenide), with varying amounts of cobalt, replacing some of the iron. Then they subjected the crystals to miniscule magnetic probes to see how they would react. They took readings mere microns apart across the face of each crystal. "This gave us information about how many superconducting electrons were actually in a superconducting state," explained SIMES researcher Lan Luan, first author on the paper, who recently defended her doctoral thesis based on this research. Previous experiments had been able to capture data only across the bulk of a material, Luan explained, but the "spot measurements" her team took gave a more detailed look into the electronic and superconductive behavior of the pnictide. Read more... Word of the Week: Meissner EffectOne of the most striking characteristics of a superconductor—aside from the fact it conducts electricity without resistance—is its ability to almost completely expel an external magnetic field. This ability is due to the Meissner Effect, named after German physicist Walther Meissner, in which the superconductor responds to an external magnetic field by setting up an electric current near its surface. The surface current generates its own equal and opposite magnetic field—thus canceling the applied magnetic field in the interior of the superconductor—and the very nature of a superconductor ensures that the current continues to flow indefinitely. The magnetic probe used in a recent SIMES study ("SIMES Researchers Find Magnetic Link to High-temperature Superconductivity," above) measured pinpoint Meissner Effects across the face of the superconducting iron pnictide crystal. |
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