Measurements of the absolute value of the penetration depth in high-T-c superconductors using a low-T-c superconductive coating

A method is presented to measure the absolute value of the London penetrati on depth, lambda (T=0), from the frequency shift of a resonator. The techni que involves coating a high-T-c superconductor with film of low-T-c materia l of known thickness and penetration depth. The method is applied to obtain lambda (YBa2Cu3O7-delta)approximate to 1460 +/- 150 Angstrom, lambda (Bi2S r2CaCu2O8+delta)approximate to 2690 +/- 150 Angstrom and lambda (Pr1.85Ce0. 15CuO4- (delta))approximate to 2790 +/- 150 Angstrom. lambda (YBa2Cu3O7-del ta) from this method is very close to that obtained by several other techni ques. For both Bi2Sr2CaCu2O8+delta and Pr1.85Ce0.15CuO4-delta the values ex ceed those obtained by other methods. (C) 2000 American Institute of Physic s. [S0003-6951(00)00148-0].