Effects of disorder on the superconducting properties of BaFe1.8Co0.2As2 single crystals

Single crystals of superconducting BaFe1.8Co0.2As2 were exposed to neutron irradiation in a fission reactor. The defects introduced decrease the superconducting transition temperature (by about 0.3 K) and the upper critical field anisotropy (e.g. from 2.8 to 2.5 at 22 K) and enhance the critical current densities by a factor of up to about 3. These changes are discussed in the context of similar experiments on other superconducting materials. (Some figures in this article are in colour only in the electronic version)