Microstructure and temperature dependence of microwave penetration depth of Ag-YBa2Cu3O7-δ thin films

The authors report the measurements of the magnetic penetration depth λ(T) of Ag-doped YBa2Cu3O7-δ (YBCO) thin films in the film thickness range 1,500--4,000 A and temperature range 18--88 K. The films are in situ grown by laser ablation on LaAlO3 <100> single crystal substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of λ(T) with the film microstructure observed with Atomic Force Microscopy has shown that λ(T) depends critically on the film microstructure. Temperature dependence of Λ(T) has also been studied for best quality films. The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without impurity scattering. The results are found to be best fitted to the d-wave model in dirty limit with impurity scattering. Near Tc, they have also compared the (3D) XY critical regime and the Ginzburg-Landau (GL) behavior