"We've shown how to grow quality, single-crystal thin films of this class of materials, so people can study the fundamental properties and limits of them," says Chang-Beom Eom, a UW-Madison professor of materials science and engineering, who led the collaboration between UW-Madison and teams from the National High Magnetic Field Laboratory and the University of Michigan
Recently, scientists have discovered an alternative to copper-oxide superconductors. Called pnictides, the materials are based on iron and arsenide and are promising because they have relatively high transition temperatures, along with other ideal properties.
Until now, no one has been able to study the intrinsic properties of pnictides because it has been impossible to fabricate a single crystal of it with all of the material grains pointing in the same direction.
The researchers then engineered a thin template to place on top of the oxide substrate. This template has both metallic and oxide elements, meaning it can interface with both the substrate and the thin film. With the template, the film grows in a more ideal arrangement. The template also acts as a nucleation layer, or barrier, between the conducting thin film and the non-conducting, or insulating, substrate.
Previously, researchers were only able to measure 10,000 amps of electricity per .06 cubic inch, which is a relatively useless amount. With the template, which is made of barium titanate or strontium titanate, Eom's team has demonstrated that pnictide thin films are capable of producing 5 million amps per .06 cubic inch — a 500-fold increase that brings pnictide current capacity into the usable range.
The team's three-pronged research — including the hypothesis about why previous approaches failed, the new template engineering solution and the significant carrying capacity results — will help other researchers learn more about pnictides and expand basic knowledge about superconductivity in general. Beyond superconductors, the template approach can be applied whenever a researcher wants to grow a metallic film on an oxide substrate.
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