Microwave surface impedance measurements of epitaxial Bi2Sr2CaCu2O8+x films grown by LPE

Precise measurements of the surface impedance Z(s) = R-s + iX(s) of Bi2Sr2CaCu2O8+x superconducting films as a function of temperature and r.f. magnetic field are reported. The samples are grown by Liquid-Phase-Epitaxy (LPE) on LaAlO3 and Th:LaAlO3 (100) substrates. The measurements are performed by a meander-line microstrip resonator operating at 2 GHz. All the samples show high residual losses (R-s = 0.4 m Ohm at T = 4.2 K). The temperature dependence of the ab-plane penetration depth has a quadratic behavior at low temperatures. The microwave power dependence of the surface impedance shows evidence of vortex penetration in weak links inside the films.