Robert B. Hallock, Ph.D. - US grants

Interesting and timely experiments in the areas of helium 3 and helium 4 mixture films, localization, and the behavior of helium in restricted/disordered environments will be performed. In each case, the vehicle to the phenomenae of interest is a helium film and in a number of situations the experiments address questions which transcend the helium community. They will study mixture films by means of the combination of NMR and third sound techniques with a focus on an elucidation of the advent of interactions among the helium 3. In the area of localization, they seek to observe and study frequency dependent localization and correlation effects in two dimensions predicted by emerging theory. In other work, they seek to study the properties of helium in cylindrical and disordered media.

Funds are requested for the purchase of equipment of critical importance for the pursuit of experiments in the area of low temperature physics at the University of Massachusetts. The equipment will permit interesting and timely experiments in the areas of: films of 3He/4He mixtures; localization; and the behavior of helium in restricted/disordered environments.

Major emphasis will be on a study of films of 3He-4He mixtures by means of a combination of NMR and third-sound techniques to elucidate the interactions among the 3He atoms and the energetics of the 3He in the confining 4He environment. Other studies will include third-sound pulses in collision and the wetting of alkali metal surfaces by helium.

This low temperature project seeks to understand the unique properties of helium films and to use these films to address problems of interest in Condensed Matter Physics. A primary objective is to study new aspects of the He-3-He-4 mixture film system. This work would include confirmation of two-dimensional Fermi liquid parameters and a search for a new superfluid state in the two dimensional 3He atop a 4He film at very low temperatures. Experiments are also conducted with helium films on patterned substrates in one and two dimensions. Topics of interest include two-dimensional localization and a possible shift of universality class due to an implied film flow. Experimental techniques include quartz crystal microbalance resonance, heat capacity studies of the thermal properties of He-4 and He-3-He-4 mixture films, and third sound studies of helium films on patterned substrates. In addition to contributing to progress in understanding the behavior of helium films themselves, the work has relevance to phenomena such as Fermi systems, localization, and two-dimensional phase transitions. It also provides excellent training for graduate students and undergraduates. The students gain experience in cutting edge technology and fundamental concepts that prepare them for careers in academe, government or industry.

This research investigates the remarkable properties of liquid helium. Such study provides unique insights into nature that are not available by the study of any other substance. Study of the wave character of thin helium films on surfaces, that have been deliberately patterned, allows an enhanced understanding of how waves can be trapped in novel environments and of how an imposed flow can modify this behavior. The study of thin film mixtures of the two naturally occurring forms of helium is motivated by theoretical suggestions that a new kind of superfluid film may be found. These studies with mixture films also allow insight into the physics of two-dimensional systems. Students involved in this work gain hands-on research experience with sophisticated instrumentation. This training prepares them for careers in academe, government or industry.

9810007 Hallock This award provides partial support for a Symposium on Quantum Fluids and Solids that will be held in Amherst, MA on June 9-14, 1998 on the campus of the University of Massachusetts. The Symposium will emphasize new developments in low temperature physics in the area of quantum fluids and solids, including BoseEinstein condensation (BEC), and will have sessions devoted to instrumentation and techniques. The conference will bring together practitioners from the atomic physics community, who have been working at ultralow temperatures in order achieve BEC, and traditional low temperature physicists, who use liquid or solid helium or adiabatic demagnetization methods to achieve ultralow temperatures. The NSF support will be used to provide travel funds for graduate students or younger faculty to attend the Symposium. %%% This awards provides partial support for a Symposium on Quantum Fluids and Solids that will be held in Amherst, MA on June 9-14, 1998 on the campus of the University of Massachusetts. The Symposium will emphasize new developments in low temperature physics in the area of quantum fluids and solids, including BoseEinstein condensation (BEC), and will have sessions devoted to instrumentation and techniques. The conference will bring together practitioners from the atomic physics community, who have been working at ultralow temperatures in order achieve BEC, and traditional low temperature physicists, who use liquid or solid helium or adiabatic demagnetization methods to achieve ultralow temperatures. The NSF support will be used to provide travel funds for graduate students or younger faculty to attend the Symposium. ***

This Grant Opportunities for Academic Liaison with Industry (GOALI) provides funding to create four different teams combining faculty and graduate student scholars at the University of Massachusetts-Amherst with Kollmorgen Technology Specialists by bringing the latter to the campus for a two month, full time assignment at the University and subsequent six month period of part-time interaction. Each team will focus on a different technology taking advantage of an existing alliance to advance innovative concepts that could serve as a model for other institutions in developing stronger ties between industry and academe. The technical areas to be undertaken will include: (1) Motion Technology-Components and Systems; (2) Digital Video Processing; (3) Imaging Sensors; (4) Human-Machine Interfaces; (5) Real Time Software, Embedded Computer and Logic Devices; and (6) Advanced Structures and Materials. Industry/Academic teams will expose faculty and students in the industry perspective and the integrative skills needed by engineers in the market. The University will gain short-term research participants who have been designated by Kollmorgen to be in-house experts in the technologies undertaken during the project. The presence of industry specialists in the laboratories and the integrative program support will act as a catalyst for faculty and graduate student teams to broaden their scope and consideration of research applications at the same time.

The industry residency and team creation program is designed to help bridge the gap between practice and scholarship in rapidly changing fields of technology. The research includes an assessment component to examine the milestones of the effort at the nine-month and eighteen-month points of progress. The lessons learned will be shared with other research and academic organizations upon which to build long term research and support models.

A top-loading dilution refrigerator and magnet system will be acquired to serve as a shared facility between four research groups. This system will provide a combined environment of extremely low temperatures (15 mK or less) and high magnetic fields (up to 10 T). It will permit relatively rapid and uncomplicated sample changes, which will facilitate sharing the facility between the research groups and will make it possible to engage undergraduates in research projects using this system. The refrigerator/magnet system will be used to study a variety of quantum phenomena at low temperature: nanoscale devices (crossed Andreev reflection devices and nanowire arrays), entangled states of molecular magnets, macroscopic quantum phenomena in SQUIDS, exotic states in quantum-fluid films, spin dynamics of quantum fluids, and cryogenic production of hyperpolarized contrast agents for MRI. Broader impacts will include opening new areas of low-temperature research to participation by undergraduates, and laying the scientific groundwork for future nanoscale, quantum-information, and hyperpolarized MRI technologies.


A specialized refrigerator and magnet system will be acquired, which will make it possible to cool samples to within fifteen thousandths of a degree from absolute zero temperature while subjecting them to extremely large magnetic fields (up to ten tesla, or about 200,000 times larger than the Earth's field). Four research groups will share this system and use it to study quantum phenomena at low temperature. The areas to be studied will include nano devices, phenomena of potential use for quantum computing, and other exotic quantum systems. A special feature of this refrigerator/magnet system is the ability to quickly and easily change samples without disassembling the entire system. This will make it possible to engage undergraduate students in research using the refrigerator, opening up new areas of physics to undergraduate physics instruction and research.

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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.

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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.

****NON-TECHNICAL ABSTRACT****
This project is focused on the use of liquid helium to study fundamental aspects of helium as well as using helium's unusual properties to explore important questions in the broader area of Condensed Matter Physics. Very thin films of helium become a friction-free superfluid at temperatures lower than about 456 degrees below zero Fahrenheit, and support waves, which act much like tiny tidal waves. Localization, a phenomenon in which waves are confined by a disordered environment, is a phenomenon of widespread importance. This importance reaches from the fundamental (the behavior of atoms in optical traps) to the applied, (the behavior of light in the technological areas of signal processing and the field of photonics). This project seeks experimental evidence for a change in the fundamental localization behavior of waves on a thin film of helium in a non-orderly environment when a direct flow of the fluid that supports the waves is applied. In another direction, earlier work has shown that when a thin film of the two kinds of helium atoms (the rare helium-3 and the more common helium-4) is atop a smooth solid hydrogen surface at low temperature there is an unexpected decoupling of atoms from the surface in addition to the usual superfluid decoupling. This suggests the exciting possibility that there may be a new type of low temperature transition that takes place in such films, different from the usual superfluid transition. The students, from graduate school down to high school, involved in these studies will gain experience in fundamental physics and cutting-edge technology. They will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.

****TECHNICAL ABSTRACT****
This project is focused on the use of liquid helium to study fundamental aspects of helium as well as using helium's unusual properties to explore important questions in the broader area of Condensed Matter Physics. The former studies will probe the unusual and unexplained de-coupling of helium atoms (in addition to the Kosterlitz-Thouless decoupling) from a weak binding substrate, specifically solid hydrogen, when a mixture of 3He and 4He is present. This decoupling suggests the exciting possibility that there may be a new type of low temperature transition that takes place in such films, different from the usual superfluid transition. A second focus will be the investigation of helium films in the presence of disorder. Third sound waves on thin films of superfluid 4He will be used to study classical wave localization on randomly patterned surfaces. It is predicted that the imposition of a flow field in the helium film will change the localization behavior. The results of this study have a potential to impact the study of the physics of cold atoms in optical potentials and the localization of light and signal processing in the field of photonics. The students, from high school through graduate school, involved in this research will gain experience in fundamental physics and cutting-edge technology. They will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.

****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.

****Technical Abstract****
This project is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: What is the mechanism by which 4He atoms are apparently able to flow though solid 4He? Prior controversial work by others has suggested that there may be a "supersolid" state of matter that may exist in solid 4He at very low temperatures. This is an issue that 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. 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. Some believe that a previously unknown plasticity mechanism may be at work. The experimental approach used in this research is to impose a chemical potential gradient on the solid by a unique technique: for example, application of a pressure difference to liquid helium that interfaces the solid instead of applying pressure directly to the 4He crystal lattice; or, the application of a temperature difference to utilize the superfluid Fountain Effect. The 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. Studies as a function of temperature and pressure (and 3He impurity concentration) will provide further evidence for flow and limit the set of possible mechanisms that are responsible for flow. The students (undergraduate, graduate) and post-graduate (postdocs) involved in these studies will gain experience in fundamental physics and cutting-edge technology. Graduating students will be poised to contribute to scientific research and technological development in industrial, national laboratory, and academic settings.

****Non-Technical Abstract****
This research is centered on an investigation of a fundamental and important current question in Condensed Matter Physics: What is the mechanism by which 4He atoms are apparently able to flow though solid 4He? Prior controversial work by others has suggested that there may be a "supersolid" state of matter that may exist in solid 4He at very low temperatures. This is an issue that 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. Some believe that a previously unknown plasticity mechanism may be at work. Most agree that disorder in the solid is a crucial ingredient. The approach used in this research is to impose, for example, 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 superfluid liquid helium that interfaces the solid on its sides using the unique properties of superfluid helium in a porous material that contains the superfluid. Participating undergraduate, graduate and post-graduate (postdocs) students will gain experience in fundamental physics and cutting-edge technology. These investigations may lead to advances in materials science that could have significant technological implications, for example in metallurgy.

****Non-Technical Abstract****
Solid 4He is a quantum solid (i.e. the properties are dominated by quantum effects) with unique properties. For example, 4He atoms are apparently able to flow though solid 4He as they do through a liquid. Prior work suggested that this behavior indicated a "supersolid" state of matter analogous to superfluidity and superconductivity. This is no longer believed to be the case but the mechanism allowing atoms to flow through the solid remains a mystery. In this project a different approach to study the flow of atoms will be used. A pressure difference will be applied across the solid by a unique technique that does not employ pushing on the crystal sides. Using this technique we will study the properties of this fascinating system as a function of flow rate and 3He concentration. Participating undergraduate, graduate and post-graduate (postdocs) students will gain experience in fundamental physics and cutting-edge technology and be prepared for future work in research, teaching or industrial settings. These investigations may lead to advances in materials science that could have significant technological implications, for example in metallurgy.

****Technical Abstract****

This project is centered on an investigation of a fundamental and important question in Condensed Matter Physics: What is the mechanism by which 4He atoms are apparently able to flow through a sample cell that is filled with solid 4He? Prior work by others initially suggested that there may be a bulk "supersolid" state of matter that may exist in solid 4He at very low temperatures. This is an issue that 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. 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. The experimental approach used in this research is to impose a chemical potential gradient on the solid: for example, by application of a pressure difference to liquid helium that interfaces the solid instead of applying mechanical pressure directly to the 4He crystal lattice; or, the application of a temperature difference to utilize the superfluid Fountain Effect to drive the flow. The approach employs the known behavior of 4He to remain a liquid at elevated pressure in the porous material Vycor (a porous glass), at pressures at which bulk 4He would be a solid. Studies as a function of temperature and pressure (and 3He impurity concentration) provided further evidence for flow of the liquid-solid melting curve. The specific mechanism for this flow will be explored including an exploration of the mechanism by which the presence of 3He dramatically suppresses the flow at a concentration-dependent temperature. One approach will be to understand how the flow responds when the solid is subjected to calibrated applied stress that deforms the solid. Another approach will be to increase the sensitivity and explore questions about the possibility of a critical flux and a possible onset of measurable dissipation. Yet another approach will be to explore the extent to which pressure suppresses mass injection and the growth of the solid in the presence of flow under various conditions. The students (undergraduate, graduate) and post-graduate (postdocs) involved in these studies will gain experience in fundamental physics and cutting-edge technology. Personnel who leave the group will be poised to contribute to scientific research and technological development in industrial, national laboratory, or academic settings.