Quantum phenomena in condensed atomic and molecular hydrogen

非技术性说明：氢原子中的自旋电子表现为微小的磁体，当嵌入固体分子氢中时，它们可以相互作用，从而形成磁相。根据量子力学，氢原子可以隧穿氢分子的晶格。在足够低的温度和足够高的密度下，嵌入分子氢晶格中的氢原子具有量子重叠，这可能导致称为玻色-爱因斯坦凝聚的现象，其中单个原子失去其身份，整个系统表现得像单个量子波。这导致了超流体性质，如无摩擦流动。本研究的一个目标是在最低温度下研究固体分子氢中的氢原子，以寻找嵌入固体分子氢中的氢原子的玻色-爱因斯坦凝聚和随后的超流行为。如果成功，该项目将开创凝聚态物理学的一个新领域，并使研究化学反应的化学家受益。第二个目标是观察分子仲氢团簇中的超流性，作为玻色-爱因斯坦凝聚的另一个证明。研究生在用于达到远低于1 K的温度的技术方面得到广泛的培训。积极的推广计划，包括讲座，与高中教师和演示会议期间进行得克萨斯州A M大学物理节。该项目还与芬兰的低温小组保持国际合作。技术说明：该研究项目的基本目标是观察嵌入固体分子氢膜中的氢原子系统中的新量子现象。这些氢原子即使在低于1 K的温度下也保持离域，如果冷却到足够低的温度，可能会表现出玻色-爱因斯坦凝聚和超固态。这项工作涉及稀释制冷机与Pomeranchuk冷却阶段相结合，将固体分子氢中的氢原子样品冷却到1 mK，预计将发生新的量子现象。氢原子基态布居和玻色-爱因斯坦凝聚的可能发生可以通过使用128 GHz的电子自旋共振技术进行探测。最近在T=0.1- 0.8K的固体分子氢膜中发现了氢原子的核极化相，这意味着可能的量子跃迁。将实验扩展到较低的温度应该有助于揭示这些相的起源及其与氢原子玻色-爱因斯坦凝聚的可能关系。此外，氢原子在固体分子氢中的空间量子扩散的研究正在进行中，这使得可以确定氢原子的有效质量和估计玻色-爱因斯坦凝聚的起始温度。该项目的第二个目标是在含有大量小仲氢团簇的宏观样品中寻找氢超流性。在0.15K下，实验观察到了包裹在氦纳米液滴中的单个仲氢团簇的超流性。研究了生长在石英微天平表面的多孔固体氖膜中的一系列小的仲氢团簇的超流性。仲氢团簇中超流性的开始被记录为通过转变温度时的微天平频率变化。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.