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Ultrasound Attenuation due to Order Parameter Fluctuations in Impure p-Wave Superconductors

The peak in the attenuation of longitudinal ultrasound in UBe13 and UPt3 below the superconducting transition has been taken as evidence for unconventional superconductivity. By studying two particular p-wave states and their collective degrees of freedom in the presence of finite quasiparticle mean free paths ℓ we show that such an interpretation of the attenuation peak is indeed feasible. Even in the hydrodynamic limit qℓ≪1 and for sound frequencies ωs/2π much less than typical collective mode frequencies, real order parameter fluctuations yield attenuation peaks in reasonable agreement with experiment, if an energy dependent normal state density of states is assumed, as seems appropriate for heavy fermion systems.