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Physicists Induce Superconductivity In Non-Superconducting Materials (phys.org)
An anonymous reader quotes a report from Phys.Org: Researchers at the University of Houston have reported a new method for inducing superconductivity in non-superconducting materials, demonstrating a concept proposed decades ago but never proven. The technique can also be used to boost the efficiency of known superconducting materials, suggesting a new way to advance the commercial viability of superconductors, said Paul C.W. Chu, chief scientist at the Texas Center for Superconductivity at UH and corresponding author of a paper describing the work, published Oct. 31 in the Proceedings of the National Academy of Sciences. The research, demonstrating a new method to take advantage of assembled interfaces to induce superconductivity in the non-superconducting compound calcium iron arsenide, offers a new approach to finding superconductors that work at higher temperatures. Superconducting materials conduct electric current without resistance, while traditional transmission materials lose as much as 10 percent of energy between the generating source and the end user. That means superconductors could allow utility companies to provide more electricity without increasing the amount of fuel used to generate electricity. To validate the concept, researchers working in ambient pressure exposed the undoped calcium iron arsenide compound to heat -- 350 degrees Centigrade, considered relatively low temperature for this procedure -- in a process known as annealing. The compound formed two distinct phases, with one phase increasingly converted to the other the longer the sample was annealed. Chu said neither of the two phases was superconducting, but researchers were able to detect superconductivity at the point when the two phases coexist. Although the superconducting critical temperature of the sample produced through the process was still relatively low, Chu said the method used to prove the concept offers a new direction in the search for more efficient, less expensive superconducting materials.
Superconductivity is a second order phase change, so yes, it would appear to be binary from the measurement perspective. Traditional LTS superconductors will conduct without loss in all three dimensions as one would expect. The common HTS superconductors the cuperates, actually only super-conduct in 2-d planes. This is one of the reasons that we have had such a difficult time getting practical high current wires and cables out of HTS that even begin to approach their small scale single grain properties.
Ok logged on and I fogot to tie the above comment to the article. Just as the aligned crystal structure in YBCO (for example) only gives you 2-D planes, it is the interface between the 2 materials in the article and their interactions that give you a 2-D superconducting plane. But just like any other superconductor, get it too hot or put it in a high magnetic field and it will change to a normal phase
Although superconductivity is a a binary effect - resistance is either identically zero or some positive value - there are practical limits. The critical temperature is one such limit that could be "boosted" - raising the temperature at which you can get superconductivity.
Another limitation that could be boosted is the current limit: although superconductors exhibit zero resistance, they cannot conduct infinite amounts of current. Try to move too much current through the material and you'll eventually have the superconductivity suddenly stop.
A third limitation of superconductors has to do with magnetic strength: a superconductor will stop being a superconductor in a sufficiently high magnetic field. I do not know for certain (I am not a solid-state physicist), but I suspect it is related to the limitations on current density.
One very practical result of these limitations is that the main magnet of MRI scanners remains quite large. They have gradually been able to increase the strength of the main field - 3 Tesla is pretty standard these days - but the magnets themselves are still really big, have relatively small (claustrophobic) bores, and are cooled using liquid nitrogen. "Boosting" conventional superconductors to be able to handle higher temperatures, higher current densities, and greater magnetic fields would presumably allow MRI's main magnet to be physically smaller, have a larger-diameter bore, be cooled with something other than helium, while maintaining or increasing the field strength.
It is notable however that they had superconducting at 350C because of this phase transition.
They annealed the material at 350C. The superconducting critical temperature of the resulting material was "relatively low", which in this context probably means that it requires cooling with liquid nitrogen or helium. If they had managed to create a superconductor that worked at 350C this would be much bigger news—we still don't know of any materials which superconduct at room temperature, much less a bit above the melting point of lead. The highest-temperature superconductor on record is hydrogen sulfide at 203K (-70C).
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