Quantum phenomena in condensed atomic and molecular hydrogen

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Non-technical description: Spinning electrons in hydrogen atoms behave as tiny magnets which can interact when embedded in solid molecular hydrogen leading to formation of magnetic phases. Hydrogen atoms can tunnel through the lattice of molecular hydrogen according to quantum mechanics. At low enough temperatures and high enough densities, the hydrogen atoms embedded in the lattice of molecular hydrogen have quantum overlap which can lead to a phenomenon called Bose-Einstein condensation, in which individual atoms lose their identities and the whole system behaves like a single quantum wave. This leads to superfluid properties such as flow without friction. A goal of this research is to study hydrogen atoms in solid molecular hydrogen at the lowest temperatures to look for Bose-Einstein condensation and subsequent superfluid behavior of hydrogen atoms embedded in solid molecular hydrogen. If successful, this project could initiate a new field in condensed matter physics and benefit chemists studying chemical reactions. A second goal is the observation of superfluidity in the collection of molecular para-hydrogen clusters as another demonstration of Bose-Einstein condensation. Graduate students get extensive training in techniques used to attain temperatures well below 1 K. Active outreach programs including lectures, meetings with high school teachers and demonstrations are performed during the Texas A&M University Physics Festival. The project also maintains the international collaboration with the low temperature group in Finland.Technical description: This research project pursues the fundamental goal of observing new quantum phenomena in a system of hydrogen atoms embedded in solid molecular hydrogen films. These hydrogen atoms remain delocalized even at temperatures below 1K and may exhibit Bose-Einstein condensation and supersolidity if cooled to low enough temperatures. This work involves a dilution refrigerator combined with a Pomeranchuk cooling stage to cool the samples of hydrogen atoms in solid molecular hydrogen down to 1 mK, where new quantum phenomena is expected to occur. The hydrogen atom ground state population and possible onset of Bose-Einstein condensation can be probed by using 128 GHz electron spin resonance techniques. The recent discovery of the nuclear polarized phases of hydrogen atoms in solid molecular hydrogen films at T=0.1-0.8 K implies possible quantum transitions. Extending the experiments to lower temperatures should help throw light on the origin of these phases and their possible relation to hydrogen atom Bose-Einstein condensation. Additionally, studies are in progress of hydrogen atom spatial quantum diffusion in solid molecular hydrogen which allows determination of hydrogen atom effective mass and estimation of the onset temperature for Bose-Einstein condensation. The second goal of the project is the search for hydrogen superfluidity in macroscopic samples containing a large number of small para-hydrogen clusters. Superfluidity of single small para-hydrogen clusters encapsulated in helium nanodroplets was observed experimentally at 0.15 K. The search for superfluidity of para-hydrogen molecules is performed for a collection of small para-hydrogen clusters embedded in porous solid neon films grown on the surface of a quartz microbalance. The onset of superfluidity in para-hydrogen clusters is registered as a microbalance frequency change while passing through the transition temperature.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.