At some point in our daily lives, almost all of us have heard of superconductors. These materials conduct electricity very well – with almost zero resistance. In comparison with normal wires carrying electricity, superconductors – because they offer no resistance – are almost loss-free. The caveat – superconductors need to be cooled to very low temperatures, making them almost impossible to operate at regular operating temperatures.
However, the situation may be about to change. Argonne National Laboratory has been researching on superconductors. Lately, scientists there have discovered that iron arsenics, a special class of superconductors, have a unique phase that has remained undiscovered so far. Using iron arsenics as a superconductor material may make it possible to harness the capabilities of energy efficient power transmission and use it in addition for a wide range of other technologies as well.
Electricity conduction is dependent on electrons, atoms and their interactions. Superconductivity occurs when these atoms and electrons behave in a special way, mostly at very low temperatures also called cryogenic temperatures.
The new discovery is about a magnetic phase of the electrons and atom interaction. This has offered significant implications over our understanding of unconventional superconductivity.
The new material is BAFe2As2 and scientists have doped 24% of the barium sites on the material with sodium. When neutrons are diffracted from a polycrystalline sample of the doped material, three different diffraction peaks are observed. These peaks vary with temperature as the magnetic and atomic structures change. In the graph, the structures are shown on the right, the blue balls represent the iron atoms and the red arrows show the direction of their magnetic moments.
Although superconductors allow electric current to flow without any resistance, they are not used for power transmission lines because they require to be cooled to cryogenic temperatures to operate efficiently. In comparison, copper wires operate at normal ambient temperatures and since they have resistance, are not loss-free. The recently discovered specific range of unconventional superconductors may soon offer better prospects.
Researchers at Argonne are trying to figure out how the new unconventional superconductor works. This knowledge might help to raise the temperature at which superconductors work, paving the way for harnessing their power for a wider range of new technologies.
In conventional metals carrying current, electrons bounce off atoms, thereby producing heat. In conventional superconductors, electrons – instead of repelling each other – pair off by binding together. This distorts the surrounding atoms, helping each other to travel through the metal. In the new type of superconductors also, the main process is still electron pair formation, but it is yet to be discovered what binds them together.
Normally superconductors have to be coaxed into allowing free flow of electricity. Although iron arsenide is normally magnetic, addition of sodium suppresses the magnetic behavior. As the material is cooled, it turns superconductive at roughly below -400 degree F, the transition temperature. Where, at room temperatures, iron atoms form a square lattice with a four-fold symmetry, at the transition temperature, this distorts to a rectangular lattice and a two-fold symmetry.
However, close to the onset of superconductivity, the new material demonstrates a phase where it returns to its four-fold symmetry. This is the phase intriguing the researchers.
