Third Sound in Superfuild 3He

Cornell University, Ithaca NY

Investigators

Abstract

9971502 Davis This is a condensed matter physics project that investigates quantum phenomena in liquid helium. Surface waves usually cannot occur on the thin liquid films which are adsorbed on solid substrates because viscosity inhibits their motion. However, in the special case of thin superfluid 4He films, these surface waves can exist and are given the name "Third Sound". This laboratory recently observed similar surface waves in thin superfluid 3He films. The discovery of third sound in superfluid 3He creates several exciting new opportunities because 3He is an unconventional p-wave Bardeen-Cooper-Schrieffer (BCS) superfluid. In some respects the complexities of the p-wave system are echoed in the more recently discovered d-wave high-Tc superconductors where the superconductivity may originate in a single 2-dimensional (2-d) atomic layer (CuO2). Thus, understanding of 2-d unconventional superconductors is both of fundamental and practical interest. Superfluid 3He, in very thin films, is an unconventional 2-d superfluid which will be investigated using third sound. Studies of quantum phase transitions are among the area of interest in this and related superconductor/superfluid research. The wide variety of experimental tools used in this research will provide an opportunity for training graduate students and post-docs in sophisticated research techniques. This experience will allow them to contribute to the nation's technological infrastructure. %%% This is a condensed matter physics project that investigates quantum phenomena in liquid helium. Waves on the surface of a fluid provide a powerful tool for studying the fluid itself and the surrounding physical environment. For example, the decreasing speed of ocean waves as they approach the shore reveals the depth of the sea and the strength of gravity. Although gravity is a common restoring force, others exist, including the electrostatic force which causes a thin liquid film to adhere to a solid. Such forces are the basis for all adherence of liquid films to solids. Previous investigations of surface waves in helium have been restricted to the 4He isotope where the superfluid waves are said to propagate via so-called 'third sound'. However, this project is focuses on the recent discover of third sound in 3He. The quantum properties of 3He differ significantly from those of 4He and present a number of new research opportunities. The physics of the 3He surface is a close counterpart to a number of technologically important thin film systems including high-Tc superconductors and the 2-dimensional electron gas in MOSFET transistors. Third sound in 3He will be used as a tool to probe the fundamental quantum physic of thin liquid films. The wide variety of experimental tools used in this research will provide an opportunity for training graduate students and post-docs in sophisticated research techniques. This experience will allow them to contribute to the nation's technological infrastructure.