Unrenormalized ultrasound attenuation in the heavy Fermion state.

Quantitative studies of ultrasound absorption in the heavy Fermion state of UPt(3) and UBe(13) are reported. The magnitude of the absorption in the normal state is not enhanced compared to ordinary metals, indicating a cancellation of the mass enhancement by a reduction of the electron-phonon coupling parameter. The T(2) variation of the normal state sound velocity at lowest temperatures is consistent with the large electronic specific heat.