Identification of multiphasic and weak-link structures in a (La0.94Sr0.06)2CuO4 single crystal by magnetically modulated resistance.

Magnetically modulated microwave and dc-resistance measurements on a (La{sub 0.94}Sr{sub 0.06}){sub 2}CuO{sub 4} crystal show that these techniques, combined with measurement of the corresponding unmodulated resistances, constitute a simple and reliable method for examining superconductor crystals both for the presence of multiple phases with different {ital T}{sub {ital c}}'s and also for the presence of weak links between different superconducting regions. Comparison of the dc and microwave results clearly demonstrates the ability of microwave measurements to assess the experimentally important surface regions of a crystal, in contrast to dc resistance, which probes the best superconducting path through the crystal. These methods can also identify weak links and determine their orientation, as illustrated by the finding of {ital b}-axis-oriented weak links in the crystal.