The correlation of the critical current density and surface resistance of YBa₂Cu₃O_7-δ thin films

We have examined the correlation between the critical current density (J_c) and the surface resistance (R(s)) of an YBa₂Cu₃O_7-δ (YBCO) thin film. YBCO films were prepared in an inductively coupled plasma sputtering system on MgO and BSO/MgO substrates. BaSnO₃ (BSO) was used as a buffer material for the MgO substrates. J_c was determined by magnetic measurements, and R_s was measured using a sapphire rod resonator method. The correlation of critical current and surface resistance has been reported previously, however, there is few researches in which a systematic correlation of R_s and J_c using the same sample has been done. To begin with, we measured R_s by the dielectric resonator method, and next, J_c was measured using the magnetic field method. As a result, it was proven that there was a strong correlation between R_s and J_c. We found that the relationship between J_c and R_s (at 22 GHz) could be expressed by the following equation, R_s = 2.0 × 10⁷J_c^-1, where the unit of R(s) is the ohm, and the unit of J_c is A/m². It was found that the relation was applicable in a wide temperature range under T_c. The value of the surface resistance can be estimated, if an accurate critical current is obtained.