c-Axis electrodynamics of YBa2Cu3O7-δ

New measurements of surface impedance in YBa2Cu3O7-delta show that the (c) over cap-axis penetration depth and conductivity below T-c exhibit behavior different from that observed in the planes. The (c) over cap-axis penetration depth never has the linear temperature dependence seen in the ab plane. Instead of the conductivity peak seen in the planes, the (c) over cap-axis microwave conductivity falls to low values in the superconducting state, then rises slightly below 20 K. These results show that (c) over cap-axis transport remains incoherent below T-c, even though this is one of the least anisotropic cuprate superconductors.