Relationship between surface resistance and critical current density of HTS thin films in a DC magnetic field

We investigated the relationship between the surface resistance (R_s) and critical current density (J_c) of DyBa₂Cu₃O_7-δ (DyBCO) thin films in a dc magnetic field. The R_s of DyBCO films at 21.8 GHz was measured using a dielectric resonator method and the J_c was determined by magnetic measurement and Bean´s model. A dc magnetic field of up to 5 T was applied along the c-axis of the films. The relationship between the R_s and J_c of DyBCO thin films under a zero magnetic field was explained by the following equation, R_s=α×10⁷/J_c, where α is a constant of 1.2, and the units of the R_s and J_c are ohm and A/m², respectively. In addition, the R_s in dc magnetic fields up to 5 T were inversely proportional to the J_c. However, the parameter α, which was fitted from the R_s-J_c characteristics in each magnetic field, increased slightly with an increase the magnitude of the applied field. These results indicate that the relationship between the R_s and J_c in a zero magnetic field may be a general property of HTS thin films and that the α in DyBCO thin films depends on the magnitude of the applied magnetic field.