Correlations Between The Critical Current-Density And Microwave Surface Impedance Of Epitaxial Yba2cu3o7-Delta Films

The microwave surface impedance and critical current density of epitaxially grown YBa2Cu3O7-delta films prepared by different techniques on MgO, SrTiO3, LaAlO3 and NdGaO3 have been measured and the correlations between them are discussed. At 77 K, in most cases, the highest J(c) values have been achieved for films with the lowest surface resistance R(s). At 4 K the surface impedance still decreases with improved sample perfection, while the critical current seems to be independent of R(s). The observed critical currents are three to five times lower than the depairing currents.