Artificially Induced Compound Defects in Cuprate and Iron-Based Superconductors

My research has been primarily focused on exploring the limits of the current carrying capacity in commercial (RE)BaCuO coated conductors, and in single crystals of the newly discovered iron-based superconductors. In particular, we use particle irradiation to create defects in these superconductors and investigate the critical current and magnetic response of the superconductor in order to identify the optimum defect structure, morphology and concentration that could lead to the highest critical current in magnetic fields. We demonstrated that the use of compound defects can greatly enhance the critical current in these materials, creating an effective enhancement over a wide field range, leading in some cases to a nearly field-independent critical current up to 7T. In single crystal iron based superconductors, we were able to demonstrate enhancements of up to 20x the pristine critical current, and in YBCO coated conductors, the use of compound defects doubled the critical current over and effective field range of 1-7T. Additionally, the use of oxygen irradiation allowed us to double the critical current in high (6T) fields in rapid irradiation times of 1s/cm2, a target for industrial application. Understanding the complex pinning landscape formed from compound defects in superconductors will be a key component to fine tuning the critical current enhancement in iron-based and cuprate superconductors. This thesis is dedicated to investigating these findings in detail.