Mass transport through solid helium

固体氦的质量传递

基本信息

批准号：
1707340
负责人：
Moses Chan
金额：
$ 46.78万
依托单位：
Pennsylvania State Univ University Park
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-07-15 至 2022-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1707340&HistoricalAwards=false
关键词：
Mass transport through solid helium

项目摘要

Non-technical abstractLiquid helium changes from a normal liquid to a superfluid at low temperatures. It is called a superfluid because it can flow with zero viscosity with no loss in energy. Once set flowing in a continuous channel, superfluid will never stop. This fascinating property is related to the fact that liquid helium enters a quantum state below 2.176 degrees Kelvin. Remarkably, recent experiments at the University of Massachusetts and Penn State found helium atoms can flow through solid helium samples like a superfluid. The Penn State team is measuring the flow rate of the helium atoms through solid helium samples of different densities, thicknesses, crystal orientations to understand the exact mechanism responsible for this phenomenon. The proposed experiments provide opportunities for postdocs, graduate and undergraduate students to receive the most rigorous trainings to be future scientists. The principal investigator and his students and post-docs are active participants in the full range of outreach activities sponsored by the Penn State Materials Research Science and Engineering Center (MRSEC) for K-12 students. These organized and coordinated outreach activities are far more effective than isolated individual efforts.Technical AbstractThe solid helium samples are sandwiched between superfluid leads in the form of porous Vycor glass cylinders infused with superfluid helium. The mass flow is thought to be related to the motion of edge dislocations and/or the transport of helium atoms through the superfluid screw dislocations in solid helium samples. Mass flow experiments through the superfluid/solid helium/superfluid "sandwiches' are in progress to test the veracity of the dislocation line model. Since dislocation lines are absent in solid helium grown inside highly porous silica aerogel, measurements in such solid samples provide a direct test on the necessity of dislocation lines for the phenomenon. Solid samples of different thicknesses ranging from 8 µm (where dislocation lines do not form a connected network) to a few mm are being studied to understand the effect of connectivity of the dislocation network. The dependence of crystal orientation is studied by affixing graphite crystals with their c-axis (which nucleates epitaxial growth of solid helium crystals) pointing either along or perpendicular to mass flow direction inside of the sample space. The mass flow through solid helium is driven by superfluid fountain pressure imposed across the samples. The flow rate as a function of temperature and the fountain pressure are measured to search for the boundary separating the dissipation-free and dissipative regions.

非技术摘要液氦在低温下从普通液体转变为超流体，因为它可以零粘度流动而不会损失能量，一旦在连续通道中流动，超流体将永远不会停止。这一性质与液氦进入低于 2.176 开尔文的量子态这一事实有关。值得注意的是，马萨诸塞大学和宾夕法尼亚州立大学最近的实验发现氦原子可以流过固体。宾夕法尼亚州立大学的团队正在测量氦原子通过不同密度、厚度、晶体取向的固体氦样品的流速，以了解造成这种现象的确切机制。所提出的实验为博士后和研究生提供了机会。首席研究员及其学生和博士后积极参与宾夕法尼亚州立大学材料研究科学与工程中心 (MRSEC) 主办的全方位外展活动。对于 K-12 学生来说，这些有组织和协调的外展活动比孤立的个人努力要有效得多。技术摘要固体氦样品被夹在注入超流氦的多孔 Vycor 玻璃圆柱体中。与边缘位错的运动和/或氦原子通过超流体螺旋位错的传输有关，在固体氦样品中通过超流体/固体进行质量流实验。氦/超流体“三明治”正在进行中，以测试位错线模型的准确性。由于在高度多孔二氧化硅气凝胶内生长的固体氦中不存在位错线，因此在此类固体样品中进行测量可以直接测试位错线的必要性人们正在研究从 8 µm（位错线不形成连接网络）到几毫米的不同厚度的固体样品，以了解位错网络连通性的影响。通过固定石墨晶体，使其 c 轴（使固体氦晶体的外延生长成核）沿着或垂直于样品空间内的质量流方向来研究晶体取向的依赖性。通过固体氦的质量流由超流体驱动。测量施加在样品上的喷泉压力。测量作为温度和喷泉压力的函数的流速，以寻找分隔无耗散区域和耗散区域的边界。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Tuning the Chern number in quantum anomalous Hall insulators

DOI：
10.1038/s41586-020-3020-3
发表时间：
2020-12
期刊：
Nature
影响因子：
64.8
作者：
Yi-Fan Zhao;Ruoxi Zhang;Ruobing Mei;Ling Zhou;H. Yi;Ya-Qi Zhang;Jiabin Yu;Run Xiao;Ke Wan
通讯作者：
Yi-Fan Zhao;Ruoxi Zhang;Ruobing Mei;Ling Zhou;H. Yi;Ya-Qi Zhang;Jiabin Yu;Run Xiao;Ke Wan

Mass transport through dislocation network in solid He4

固体 He4 中通过位错网络的质量传输