High Frequency First Sound Waves Propagating near the Normal Superfluid Transition in ~4He Liquid: A Comparison between Experiments and the Classical Critical Dynamic Theories

摘要

In this lecture an attempt is made to describe, in a general context, some of the aspects of the propagation on (first) sound waves near T_λ(P) in liquid helium. In addition to a general introduction, this paper will focus on the comparison of the high frequency data with the classical models: the order parameter relaxation mechanism of Landau and Khalatnikov, and the order parameter fluctuation mechanism of Kawasaky. Although it is now very well established that these models fails to explain the critical behaviour of first sound near T_λ(P) in liquid helium, they still serve as basic references for the actual critical dynamic theories for first sound. In addition, both approaches are still applied to many transitions in other systems. So, these two models are compared here quantitatively with the high frequency data, mainly with that obtained with a light-scattering experiment performed a few years ago.