Experiments on the Josephson plasma mode in Bi₂Sr₂CaCu₂O₈ and the thermal hall conductivity in YBa₂Cu₃O₇

The Josephson plasma mode has been observed directly in Bi₂Sr₂CaCu₂O₈ using microwave radiation in the 30 to 90 GHz range. Measurements in an oblique field provide rather conclusive evidence for the plasma oscillations, as well as a determination of the anisotropy parameter γ. In a second experiment, we discuss how the mean free path ℓ₀ of quasi-particles may be measured using asymmetric scattering off pinned vortices. In 90-K YBa₂Cu₃O₇, we find that ℓ₀ increases rapidly from 90 Å at 100 K to 2500 Å at 15 K.