New Iron-Arsenic Superconductors Created

Power transmission networks spanning long distances suffer from one major flaw, experts say, and that is the fact that they lose a large amount of the charge they carry due to the resistances the current encounters. But now, a new class of superconducting materials, known as iron-arsenide superconductors, which has only been recently proven by experts at the US Department of Energy's Ames Laboratory, may open up new avenues of research into zero-resistance power transmission. Their unique properties have made scientists place these materials in a superconducting class of their own.

Lead researcher Ruslan Prozorov, who is a physicist at the Ames Laboratory, says that the most important trait of this type of materials, which is the way in which they couple their electrons, is very different in iron-arsenide compounds than in any other class of superconducting materials. In regular materials, electrons pair in what are known as Copper pairs, which behave in exactly the same way. The uniform flow of Copper pairs is what this class of conducting materials is all about, and is the characteristic they are most famous for.

But all regular superconductors emit a very low magnetic field, which appears regardless of the measures against it employed by research teams worldwide. These fields penetrate but a narrow layer of the superconductor, a depth that has come to be known as the London penetration depth. “The change of the London penetration depth with temperature is directly related to the structure of the so-called superconducting gap, which in turn depends on the microscopic mechanism of how electron pairs are formed. London penetration depth is one of the primary experimentally measurable quantities in superconductor studies,” Prozorov explained.

As opposed to regular superconductors, where the ratio of the London penetration depth is widely studied and charted, the iron-arsenide kind exhibits a power-law – almost quadratic – temperature variation of penetration depth. Details of how this happens are published in several recent issues of the scientific journal Physical Review Letters and Physical Review B: Rapid Communications.

“This type of research requires measurements of many, nominally the same, samples in three different orientations with respect to an applied magnetic field. All along, we expected to see an exponential London penetration depth – but we didn't. So, we examined samples with different concentrations of cobalt. But we got the same results, and with data from other iron-arsenide systems, we observed a universal, nearly quadratic behavior of the penetration depth,” Prozorov added.

The expert concluded by saying that, “The iron-arsenides are probably among [the] most complex superconductors we – the superconductor research community – have encountered so far. Altogether, analysis of the data collected on many samples shows that the iron-arsenides do not adhere to the previous superconductivity theories and that something else is happening. Of course, some theoretical models do exist, and we collaborate with leading theorists, including Ames Laboratory's Jörg Schmalian, who has provided important insight into our observations. The unique qualities of the iron-arsenides cause me to believe that materials where transition temperature is closer to room temperature are possible.”