Meissner effect in Cu backed by superconducting Nb and NbTi wires

The Meissner screening length in Cu of Cu clad Nb and Cu clad NbTi wire was measured over temperature range from T sub(c) down to 25 mK. The temperature dependence of the screening length was found to be expressed by (T + T0)sup(-1/2) from about 1.5 K to the lowest temperature, rather than by Tsup(-1/2) derived by Deutscher and de Gennes for the dirty limit. The length becomes 12 μm for Cu clad Nb and 7 μm for Cu clad NbTi wire. Preliminary measurements of field and frequency dependence are also presented. (auth.)