MAGNETIC PENETRATION DEPTH OF OXYGEN-DEFICIENT YBA2CU3O7-DELTA SINGLE-CRYSTALS (TC=66-K)

For single crystals of YBa2Cu3O7-delta with T(c) = 66 K, we measured the magnetic penetration depth lambda-ab(T), with the applied magnetic field oriented perpendicular to the CuO2 Planes, using high-field magnetization isotherms M(H,T). The zero-temperature value lambda-ab(0) is about 2600 angstrom, a value almost twice that of YBa2Cu3O7-delta With T(c) = 90 K, but similar to that of Bi2Sr2CaCu2O8+delta. The temperature dependence of lambda-ab(T) reveals some deviation from the theoretical BCS weak-coupling clean limit, and from the two-fluid model. These observations are discussed and compared with magnetic-penetration-depth data for other high-T(c) superconductors.