9322389 Ellis Technical abstract: Third sound waves will be used to study the properties of vortices in superfluid 4He films at low temperatures. These vortices have been recently shown to exist well below the superfluid transition, pinned to the substrate and stable against moderate film flow. Large amplitude third sound waves not only provide film flow large enough to move the vortices, but are able to create and destroy the vortices by the quantum-mechanical analogy of swirling. Small amplitude waves are used to probe the vortex distribution. This detailed study of vortex pinning and creation will provide better understanding of the importance of innate vortices at low temperatures and their properties. Non-technical abstract: This research will investigate the properties of microscopic quantized circulation states in thin films of superfluid helium. These vortices have been shown to play a role in the properties of films near the superfluid transition temperature and will be studied directly for the first time at lower temperatures by their interaction with sound waves. Unlike its counterpart superconductivity, there remain fundamental problems in the microscopic description of the superfluid state and clarifying the role of the vortices in films will contribute to the general understanding of condensed matter physics. ***
