Meissner effect in Y-Ba-Cu-O and La-Sr-Cu-O high-temperature superconductors

Measurements of the static magnetic susceptibility confirm the existence of significant Meissner flux expulsion in the high-temperature superconductors Y/sub 1.2/Ba/sub 0.8/CuO/sub 4/ and La/sub 1.85/Sr/sub 0.15/CuO/sub 4/ below the onset temperatures of 85 and 39 K, respectively. The Y-Ba-Cu-O sample contains both superconducting and nonsuperconducting phases. The observed Meissner effect corresponds at 20 G to at least 20% of perfect diamagnetism in the black superconducting phase. For the single-phase La-Sr-Cu-O compound the Meissner signal at 10 G reaches a value corresponding to at least 24% of perfect diamagnetism.