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, λ(T=0), from the frequency shift of a resonator. The technique involves coating a high-Tc superconductor with film of low-Tc material of known thickness and penetration depth. The method is applied to obtain λ(YBa2Cu3O7−δ)≈1460±150 Å, λ(Bi2Sr2CaCu2O8+δ)≈2690±150 Å and λ(Pr1.85Ce0.15CuO4−δ)≈2790±150 Å. λ(YBa2Cu3O7−δ) from this method is very close to that obtained by several other techniques. For both Bi2Sr2CaCu2O8+δ and Pr1.85Ce0.15CuO4−δ the values exceed those obtained by other methods.