Studies of Solid 4-Helium

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** This research project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: Is it possible (and if so, what is the mechanism) for 4He atoms to flow though solid 4He. Prior work by others has suggested that this strange phenomenon might be possible and that there may be a ?supersolid? state of matter that may exist in solid 4He at very low temperatures. A ?supersolid? would represent a new quantum state of matter, therefore the question of its existence has aroused intense interest in the Condensed Matter community, stimulated a number of experiments and theoretical works, and resulted in a number of possible explanations and some substantial paradoxes. To determine whether it is possible for 4He atoms to flow through solid 4He, this project will impose a pressure difference across the solid by a unique technique that does not employ pushing on the crystal sides of the solid. Instead, application of a pressure difference is made to liquid helium that interfaces the solid on its sides. The approach employs the known behavior of 4He to remain a liquid at elevated pressure in Vycor (a porous glass). The pressure is applied to the liquid helium in the Vycor and atoms are fed into the solid helium through the interface where the Vycor meets the solid. The students involved in these studies will gain experience in fundamental physics and cutting-edge technology. They will work toward a Ph.D. degree and at graduation will be poised to contribute to scientific research and technological development in industrial, national laboratory, and academic settings. ****TECHNICAL ABSTRACT**** This research project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: Is it possible for 4He atoms to flow though solid 4He and if so, what is the mechanism. Prior work by others has suggested such flow might be possible and more specifically that there may be a ?supersolid? state of matter that may exist in solid 4He at very low temperatures. A ?supersolid? would represent a new quantum state of matter, therefore the question of its existence has aroused intense interest in the Condensed Matter community, stimulated a number of experiments and theoretical debate, and resulted in a number of possible explanations and some substantial paradoxes. The theoretical debate insists that perfect crystals of solid helium cannot be a ?supersolid?, and that any mass flux through the solid must be carried by defects. Various defect mechanisms have been proposed. To investigate the possibility of mass flux through solid 4He, this project will impose a chemical potential gradient on the solid by a unique technique: application of a pressure difference to liquid helium that interfaces the solid instead of applying pressure directly to the 4He crystal lattice. This approach employs the known behavior of 4He to remain a liquid at elevated pressure in Vycor (a porous glass), at pressures at which bulk 4He would be a solid. Application of a chemical potential difference across solid helium flanked by Vycor will allow atoms to be injected into the solid without application of a mechanical pressure difference to the lattice. Studies as a function of temperature and pressure will provide evidence (or not) for flow and limit the set of possible mechanisms that are responsible for flow. The students involved in these studies will gain experience in fundamental physics and cutting-edge technology. Upon completion of Ph.D. dissertations they will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.