Direct Measurement of the Temperature-Dependent Magnetic Penetration Depth in Y-Ba-Cu-O Crystals

The temperature dependence of the magnetic penetration depth is determined directly from low-field dc magnetization measurements on single-crystal Y-Ba-Cu-O (Tc=89.7 K, "Tc=0.2 K). The results are consistent with the behavior expected from a BCS (s wave) superconductor. © 1989 The American Physical Society.