Researchers have found that two iron arsenide superconductors exhibit novel behavior. When a material is cooled below its superconducting transition temperature in an applied magnetic field, it expels some portion of that field. Exactly how this Meissner effect occurs depends on the physical properties of the sample, the type of superconductivity, and the experimental conditions. However, for all superconductors field expulsion is determined by the strength of the Meissner currents, which peak at some critical field value. The signature of the field dependence is that the magnetization of the superconductor reaches a maximum at the critical field and then starts to decrease. In contrast, for these arsenide materials, the degree of Meissner expulsion continues to increase, almost linearly, even when the applied field far exceeds the theoretically estimated critical field value. This suggests that the Cooper pairing in iron arsenide superconductors may recover some strength because the magnetic field suppresses scattering effects. The new findings suggest further experiments that may provide additional clues as to the mechanism of superconductivity in these materials.
- R. Prozorov, M. A. Tanatar, Bing Shen, Peng Cheng, Hai-Hu Wen, S. L. Bud'ko, and P. C. Canfield. Anomalous Meissner effect in pnictide superconductors. Physical Review B 82, 180513(R), (2010). DOI:10.1103/PhysRevB.82.180513