Transport critical current measurements on a Cu-substituted BaFe ₂As₂ superconductor

The critical current density J_c is a crucial parameter to establish the actual technological potential of a superconducting (SC) material. Furthermore, being proportional to the SC gap parameter, it can reveal important information about the microscopic nature of the SC state in a given material. The FeAs-based class of SC materials has been a focus of intense scientific investigation lately, but direct investigation of J_c by transport measurements is rather scarce in literature. For these materials, it is very interesting to map J_c as a function of their distinct SC tuning parameters such as applied pressure and chemical substitution. In this work, detailed investigation of the field, temperature, and pressure dependences of transport critical current density J_c for Cu-substituted BaFe₂As₂ single crystals is reported. In this particular material, Cu-substitution has a strong magnetic pair breaking effect. However, with increasing pressure, this sample shows an almost twofold increase of T _c, from 3.2K to 6.9K, which is followed by an increase in J _c. These observations are discussed considering the presence of magnetic pinning centers in the Fe-As plane, which, in principle, could suggest effective routes to increase J_c in the this class of materials.