Condensed Matter Seminars

A family of new Fe superconductors of SmFeAsO1-xFx and others have been discovered in 2008 that contain the puckered FeAs planes instead of the hallmark CuO2 planes in the cuprate superconductors. Central to any superconductor is the nature of its superconducting gap, its value, its structure if any, its temperature dependence. We used Andreev reflection spectroscopy to investigate the gap of these new (1111) Fe superconductors and its temperature dependence. Although the gap values and transition temperatures are different for the Fe superconductors with different F doping, the values of 2 Δ /kBTC are all close to 3.53 that of a BCS s-wave superconductor. The gap is nearly isotropic with temperature dependence close to that of an s-wave superconductor. We did not find evidences of pseudogaps, but the spin density wave transition can induce spurious “pseudogaps” in the system. These characteristics of the Fe superconductors are dramatically different from those of the cuprate superconductors.