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.

在低温下，非技术抽象的氦气从正常液体变为超流体。它被称为超流体，因为它可以以零粘度流动而不会损失能量。一旦设置在连续的通道中，超级流体将永远不会停止。这种引人入胜的特性与液氦进入低于2.176度开尔文的量子状态有关。值得注意的是，最近在马萨诸塞大学和宾夕法尼亚州立大学进行的实验发现，氦原子可以流经诸如超氟的固体氦样品。宾夕法尼亚州立大学通过不同密度，厚度，晶体取向的固体氦样品来测量氦原子的流速，以了解负责这种现象的确切机制。拟议的实验为博士后，研究生和本科生提供了机会，可以接受最严格的培训，成为未来的科学家。首席研究员及其学生和职业生涯是由宾夕法尼亚州立材料研究科学与工程中心（MRSEC）赞助的全方位宣传活动的积极参与者。这些有组织的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以多孔的Vycor玻璃圆柱体的形式夹在超流体铅之间，感染了超氟化氦气。质量流被认为与边缘脱位的运动和/或氦原子通过固体氦样品中的超氟螺钉位错的运输有关。通过超级流体/固体氦/超流体“三明治”进行的质量流量实验正在进行测试，以测试位错线模型的准确性。由于在高度多孔硅胶内生长的固体氦气中不存在脱位线，因此在此类固体样品中测量的测量值是对固体类别的必需线路的必要直接测试。固体线的必需线路的厚度。正在研究少数MM，以了解晶体方向的连通性的效果。测量温度和喷泉压力的功能，以搜索将无耗散和耗散区域分开的边界。

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