Studies with Liquid Helium Films

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9819122HallockThis low temperature physics project investigates the unique properties of helium films. Of interest are the fundamental behavior of the films and their application in other studies of problems of interest in Condensed Matter Physics. New aspects of the He-3/He-4 mixture film system, including localization, measurements on hydrogen substrates, the determination of two dimensional Fermi liquid parameters, and the search for a new superfluid state in the two dimensional He-3 atop a He-4 film at very low temperatures will be investigated. The work explores capillary condensation and avalanche phenomena with helium in porous materials, and examines the relevance of current theoretical notions to such systems. Experiments are conducted with helium films on patterned substrates in one and two dimensions, with a focus on two dimensional localization. The methods include NMR, quartz crystal microbalance resonance, third sound, and heat capacity studies of the thermal properties of He-4 and He-3/He-4 mixture films, and high resolution capacitance measurements of capillary condensation and avalanche events in porous materials. In addition to contributing to progress in understanding the behavior of helium films themselves, the work has relevance to the wider community in the areas of Fermi systems, localization, two dimensional phase transitions, avalanche phenomena, and capillary condensation. It also provides excellent training for the graduate students and research participation opportunities for the undergraduates who are associated with it.%%%This research investigates the remarkable properties of liquid helium. Such study provides unique insights into nature which are not available by the study of any other substance. Thin films of helium provide information on the behavior of weak binding surfaces such as hydrogen, which aids in the understanding of the general problem of wetting of surfaces. Study of the wave character of such thin films on surfaces which have been deliberately patterned allows an enhanced understanding of how waves can be trapped in novel environments. The study of thin film mixtures of the two naturally occurring forms of helium may result in the discovery of an exciting new kind of superfluid which is predicted but has not yet been observed. Helium in its friction-free superfluid state is utilized to further understand the dramatic avalanche behavior observed when helium drains from spongy substances. These experiments allow a better understanding of the process of fluid removal from porous materials. Students involved in this work are provided with a high quality hands-on research experience using sophisticated instrumentation.