Mar
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Superconductivity Warms Up
March 4, 2013 | Leave a Comment
The new material can be tailored with seamless alternating layers of metal and oxide layers to achieve extraordinary superconducting properties. Of particular interest is the ability to transport much more electrical current than non-engineered materials.
Superconductor Superlattice Schematic Structure. Click image for the largest view.
Today’s superconductors operate only under extremely cold conditions to transport energy very efficiently. With the ability to transport large electrical currents and produce high magnetic field superconductors feed power to such existing technologies as magnetic resonance imaging. They hold great potential for emerging applications in electronic devices, transportation, and power transmission, generation and storage.
Carefully built up layered superconducting materials are increasingly important in highly sophisticated applications. For example, a superconducting quantum interference device, or SQUID, used to measure subtle magnetic fields in magnetoencephalography scans of the brain, is based on a three-layer material.
The problem remains; these things have to run very cold to stay superconductive, pushing the quest to understand and leverage superconductivity into developing materials that work at room temperature. Even the latest unconventional high-temperature superconductors operate below minus –369ºF (-223ºC).
The research team’s iron-based “pnictide” unconventional high-temperature superconductor material is promising in part because its effective operating temperature is higher than that of conventional superconducting materials such as niobium, lead or mercury.
“Pnictide” superconductors include compounds made from any of five elements in the nitrogen family of the periodic table.
The team engineered and measured the properties of superlattices of pnictide superconductors. A superlattice is the complex, regularly repeating geometric arrangement of atoms, its crystal structure, in layers of two or more materials.
The new material is composed of 24 layers that alternate between the pnictide superconductor and a layer of the oxide strontium titanate. Creating such systems is difficult, especially when the arrangement of atoms, and chemical compatibility, of each material is very different.
The researchers built up the superconductor layer after layer maintaining an atomically sharp interface – the region where materials meet. Each atom in each layer is precisely placed, spaced and arranged in a regularly repeating crystal structure.
As they grew the superlattice, the researchers also added a tiny bit of oxygen to intentionally insert defects every few nanometers in the material. These defects act as pinning centers to immobilize tiny magnetic vortices that, as they grow in strength in large magnetic fields, can limit current flow through the superconductor.
Eom explains, “If the vortices move around freely, the energy dissipates, and the superconductor is no longer lossless. We have engineered both vertical and planar pinning centers, because vortices created by magnetic fields can be in many different orientations.” This helps the new material to have improved current-carrying capabilities.
Eom sees possibilities for researchers to expand upon his team’s success in engineering man-made superconducting structures. “There’s a need to engineer superlattices for understanding fundamental superconductivity, for potential use in high-field and electronic devices, and to achieve extraordinary properties in the system,” says Eom. “And, there is indication that interfaces can be a new area of discovery in high-temperature superconductors. This material offers those possibilities.”
The importance of superconductors and the potential can be seen in a post from Brian Wang’s NextBigFuture about superconducting and propulsion. The comparison that jumps out is the differences in weight comparing industrial, likely 3 phase motors and turbines.
Click image for the largest view.
When one considers the role of weight in fuel economy, superconductors are going to be very important if not simply a necessary threshold for electric propulsion success.
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