Ultrasound attenuation in Sr2RuO4: An angle-resolved study of the superconducting gap function

We present a study of the electronic ultrasound attenuation ct in the uncon ventional superconductor Sr2RuO4. The power law behavior of cu at temperatu res down to T-c/30 clearly indicates the presence of nodes in the gap. In t he normal state, we find an enormous anisotropy of alpha in the basal plane of the tetragonal structure. In the superconducting state, the temperature dependence of alpha also exhibits significant anisotropy. We discuss these results in relation to possible gap functions.