Researchers introduced disorder to test electron pairing in iron-based superconductors and produced compelling experimental evidence supporting one particular pairing type. Superconductivity is the resistance-free flow of electrons that occurs when some materials are cooled below a critical temperature. Superconducting electrons practice the buddy system, pairing up in so-called Cooper pairs and behaving as a single particle. Importantly, there are different ways to form Cooper pairs and in iron-based superconductors there has been debate over the pairing type. In particular, is the sign of the parameter that describes the ordering of electron pairs the same (s++) or different (s±) for the different ranges of energies that electrons can (or cannot) have in a superconducting material? To test pairing symmetry, the team introduced disorder to high-quality single crystals through electron irradiation. A beam of electrons moving at almost 98% the speed of light was used to create defects; such a beam is like a small but very powerful stream of cannonballs capable of displacing ions in the crystal lattice and thus creating defects. The s++ and s± pairing react differently to this additional disorder, and this was measured by testing the resistivity of the sample. The team’s findings were fully compatible with the s± pairing type, providing strong support for superconductivity mediated by magnetic fluctuations. Because pairing symmetry is intimately related to the mechanism of superconductivity, this research provides important insight into the phenomenon of high-temperature superconductivity.
Effect of electron irradiation on superconductivity in single crystals of Ba(Fe1-xRux)2As2 (x=0.24)