Superconductivity in iron-based materials explained with electron orbitals

Superconductivity in iron-based materials explained with electron orbitals

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News & Events - Engineering News

February 14, 2014

Superconductivity is currently a hot topic in theoretical and engineering research, with many teams of scientists working to uncover its mysteries and discover new ways to produce it. A group of researchers recently found out how electron orbitals enable superconductivity to arise in materials composed of iron, Brookhaven National Laboratory reported.

Orbitals and superconductivity
In many cases, materials capable superconductivity take on the property at very low temperatures. However, superconductivity can be induced in compounds at higher temperatures by adding other elements to the mix. Iron-based substances can become superconductive by undergoing such a procedure, though the mechanics of this process are still being explored.

Research conducted by scientists at the Brookhaven Lab revealed that variations in the behavior of electron orbitals can trigger superconductivity in ferric compounds. When electricity is run through the atoms of a superconductive material, valence electrons with negative charges can be repelled and pushed into new positions within the substance. This operation, or "excitonic mechanism," can cause electrons to be sucked into a positively charged region, contributing to the pairing process that allows electrical currents to flow without resistance.

"High-temperature copper-oxide superconductors, or cuprates, contain in effect a single orbital and lack the degree of freedom to accommodate strong enough interactions between electricity and the lattice," said Weiguo Yin, a scientist with the Brookhaven Lab. "But the barium iron arsenic we tested has multi-orbital electrons that push and pull the lattice in much more flexible and complex ways, for example by inter-orbital electron redistribution. This feature is especially promising because electricity can shift arsenic's electron cloud much more easily than oxygen's."

The extra flexibility afforded by the multi-orbital electrons in the barium iron arsenic compound is due to a greater number of possible positions for electron relocation as a result of an electric current. With this improved range of electron motion, it may be possible to induce superconductivity at higher temperatures and open up new avenues for engineering research and development.

Significance of the discovery
Alterations in the electron orbitals in the barium iron arsenic can be induced by doping the material with cobalt, creating a positively charged area within the compound. In turn, this pocket gives rise to superconductive properties at a higher temperature than would otherwise be possible.

"What's really exciting is that this electron polarization exhibits strong coupling. The quadrupole polarization of the iron, which indicates the orbital fluctuation, couples intimately with the arsenic dipole polarization—this mechanism may be key to the emergence of high-temperature superconductivity in these iron-based compounds. And our results may guide the design of new materials," Yin said.

New substances that are capable of superconductivity at higher temperatures would be able to be applied more easily and for a broader range of uses than their counterparts that function at lower temperatures. Nonetheless, superconductors of both varieties could be used for numerous applications.

According to Georgia State University's HyperPhysics resources, magnets with superconductive properties can be utilized in an array of technologies, such as magnetic levitation trains, magnetic resonance imagers and superconducting quantum interference device magnetometers.

Engineering information indicates that trains that use superconducting magnets to move by repelling standard rails can be safer than conventional railroad technology. Magnets with superconductivity can also improve the functioning of MRI devices by contributing to parts-per-million spacial uniformity in human-sized spaces.

Developments in our understanding of superconductivity promises advances in numerous technological fields. As new superconductive materials are created and designed for different applications, engineering handbooks may come to include extensive information about these powerful substances within their pages.

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