SGER: An Experiment to Understand the Apparent "Supersolid" Behavior of Solid 4He

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

********NON-TECHNICAL ABSTRACT***** Recently a startling discovery was announced: At very low temperatures and elevated pressures atoms of helium apparently flow though solid helium without friction. This announcement was startling because ordinary solids behave themselves and while atoms in a solid wiggle a bit, they generally stay put. It is common experience that when you pick up a rock, none of the solid leaks out. This Small Grant for Exploratory Research (SGER) will support a project that will, under a variety of temperatures and pressures, explore whether a pressure difference applied between two liquid helium reservoirs on either side of a block of solid helium will relax by the flow of atoms through the solid helium. The reservoirs on either side of the solid will be liquid, maintained in that state by the unique properties of helium in a highly porous material. If atoms do indeed flow through the solid, this research will help to determine the true mechanism by which this takes place. And, if such flow is present, other experiments will attempt to cause the flow to take place through a donut-shaped sample of solid helium and determine whether such flow is persistent - i.e. able to flow in a closed loop without slowing down. That is, the research will explore whether it is possible for there to be friction-free super-flow in a solid. The experiments are time-urgent since this area is extremely active; with groups around the world intensely pursuing different approaches in attempts to confirm the existence of this strange state. While ripe for discovery, such work is also risky, with some experiments to date yielding unexpected negative results. Confirming the existence of this strange solid would have a large impact our understanding of "quantum states of matter." Graduate students will be involved in the experiments and thus they will receive training that will lead to a Ph.D. and their eventual entry into the scientific workforce. ******** TECHNICAL ABSTRACT***** This SGER supports research seeking to provide substantial insight into the true physics behind the startling observations of Kim and Chan seen in solid helium in which they observed a moment of inertia change in a torsional oscillator and interpreted the observation as evidence for a new state of matter, a "supersolid". The first experiments will place solid helium adjacent to helium contained in the porous material Vycor, by which it is possible to create a condition in which liquid helium can interface solid helium at pressures above the normal melting curve. The experiments will seek to establish whether a pressure difference imposed between the two fluid reservoirs on two sides of a cylinder of solid helium can relax by the flow of helium atoms through the solid and how such flow may vary with the base pressure of the solid. When completed, these experiments should shed considerable insight into the true nature of the "supersolid" and help to elucidate the specific mechanism by which such flow takes place. If such flow is detected with reasonable critical velocity, the next experiments will seek to establish a persistent flow in a torus-shaped geometry and document that the flow is indeed persistent. The experiments are time-urgent since this area is extremely active; with groups around the world intensely pursuing different approaches in attempts to confirm the existence of the "supersolid" state. While ripe for discovery, such work is also risky, with some experiments to date yielding unexpected negative results. Confirming the existence of a "supersolid" state would have a large impact on our understanding of quantum states of matter. Graduate students will be involved in the experiments and thus they will receive training that will lead to a Ph.D. and their eventual entry into the scientific workforce.