MICROWAVE SURFACE IMPEDANCE MEASUREMENTS OF EPITAXIAL BI2SR2CACU2O8+XFILMS GROWN BY LPE

Precise measurements of the surface impedance Z(s) = R-s + iX(s) of Bi 2Sr2CaCu2O8+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 measureme nts 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 dept h has a quadratic behavior at low temperatures. The microwave power de pendence of the surface impedance shows evidence of vortex penetration in weak links inside the films. (C) 1997 Elsevier Science B.V.