Fast Mode in Dense Aerogel Filled with Superfluid He II and Dilute Mixture of 3He in 4He

摘要

Longitudinal sound wave propagation in 90% porous silica aerogel filled with superfluid He II and dilute mixture of 3He in 4He has been studied using a low frequency resonance method. The observed fast mode was identified as a mode intermediate between the sound in the aerogel matrix and first sound. It was shown that the behavior of the fast mode in dense aerogel differs from both high porosity aerogel and rigid porous medium. We discuss the obtained results within the framework of theoretical models available.