Current situation in the superfluid 3He collective mode study:: experiment and theory

For a long time the study of the collective modes (CMs) has been an essential part of the experiments in superfluid He-3. But at present such kinds of experiments in superfluid He-3 are practically stopped while many very interesting features of the CM spectrum still remain unexplored by experiment. There are a few causes for this. One is the discovery of heavy fermion and high-temperature superconductors, the investigation of which drew away many scientists. From the other side most of the basic experiments with CMs have been done and the next step is to study the fine structure like the splitting of the CM spectra by electric and magnetic fields, and by dispersion, superflow, rotation and other perturbations. This step requires much longer time to prepare the experiments as well as much more skills and luck. We analyze the difficulties that arise in experiments and discuss some old and new effects in CMs in superfluid 3He which should be studied experimentally. The purpose of this paper is to call experimentalists to renew the ultrasound experiments in superfluid He-3 by attracting their attention to new possibilities in this area. (C) 2000 Published by Elsevier Science B.V. All rights reserved.