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

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