MEASUREMENTS OF SURFACE IMPEDANCE, LONDON PENETRATION DEPTH, AND COHERENCE LENGTH IN Y-BA-CU-O FILMS AT MICROWAVE-FREQUENCIES

We have improved a microwave self-resonant technique to measure surfac e resistance R(s) directly and surface inductance L(s) indirectly. For films prepared by the laser ablation technique we observed that R(s) at 21 GHz decreased by about three orders of magnitude as the temperat ure decreased from 90 to 80 K reaching a low value of 4.9 X 10(-4) OME GA. We measured the London penetration depth lambda and coherence leng th xi, and found that both lambda and xi are anisotropic. Their values depended on the direction of the microwave electric field relative to the c axis. We deduced the value of lambda(parallel-to)(0) to be abou t 1800 angstrom, lambda(parallel-to)(86.5) about 8000 angstrom, and la mbda(perpendicular-to)(86.5) about 26000 angstrom, where lambda(parall el-to)(0) is the penetration depth (as T --> 0 K) for the electromagne tic electric field parallel and lambda(perpendicular-to) perpendicular to the film plane. In addition xi(parallel-to) was determined to be 1 29 angstrom and xi(perpendicular-to) equal to 40 angstrom at 86.5 K. T he anisotropic factor gamma is about 3.