Studies of Supersolidity in Solid 4He

Cornell University, Ithaca NY

Investigators

Abstract

****Technical Abstract**** The recent discovery of a "supersolid" phase in solid 4He at temperatures below 200mK by the Eunsong Kim and Moses Chan provides the realization of a prediction made more than a quarter of a century ago. The initial suggestion for a supersolid state in crystalline 4He is based on the possibility that Bose-Einstein condensation might occur in solid helium at sufficiently low temperatures. It is crucial to establish whether or not the supersolid state represents a new type of superfluid. In an attempt to clarify this issue several approaches will be pursued. First, the hydrodynamics of the supersolid will be examined in non-circular geometries where the predicted behavior based on ordinary superfluid hydrodynamics is clear. Second, multiple frequency compound oscillators will be used to distinguish a true superfluid from effects arising from the anomaly, discovered by Day and Beamish, in the low temperature properties of the elastic shear modulus. Third, the question of the existence of a thermodynamic phase transition to the supersolid state will be addressed through measurement of the expected heat capacity anomaly associated with the transition utilizing ultra sensitive SQUID technology. This project is expected to involve one to two undergraduate students who should profit greatly from working in a fast evolving area at the current forefront of condensed matter research. ****Non-Technical Abstract**** One of the most exciting recent discoveries in condensed matter physics has been the observation of the so-called "supersolid" state at temperatures only a few tenths of a degree above absolute zero. This supersolid state has the remarkable property that a fraction of a helium solid can actually pass through itself as a frictionless flow provide the temperature is low enough. This property of the supersolid is counterintuitive and is at odds with our instinctive concept of a solid. The supersolid may be another example of a superfluid system to take its place beside the previously know superfluids; superfluid 3He and 4He, superconducting electrons, and the superfluids observed in low density trapped atomic gases. One of the most important questions to be addressed is whether the supersolid phenomena thus far observed is actual a true superfluid state in solid helium or is it a manifestation of the unusual elastic properties of the solid know to appear in the same temperature region as the supersolid phenomenon. This research project will address this question on several fronts. The approach asks the question, does the superfluid obey superfluid hydrodynamics and can the effects of elasticity be separated from those of a superfluid by multi-frequency experiments? The second approach will examine the nature of the phase transition to the supersolid state by a ultra sensitive heat capacity measurement utilizing state-of-the-art superconducting technology. These projects will involve several undergraduate students and will give them a head start in scientific research.