Properties of Superfluid Three Helium in Novel Porous Media at Very Low Temperatures

极低温下新型多孔介质中超流三氦的特性

• 批准号: 9705295
• 负责人: Jeevak Parpia
• 金额: $ 81.63万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-15 至 2001-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9705295&HistoricalAwards=false
• 关键词: Properties; Superfluid; Three; Helium; Novel

w:\awards\awards96\num.doc 9705295 Parpia This Focused Research Group grant supports a comprehensive experimental and theoretical study of the effects of nanoscale disorder on quantum ground states, including superfluid phases. The discovery that the phase diagram of mixtures of 3He and 4He is radically altered by a low density aerogel medium was rapidly followed by studies of pure 3He in aerogel. These studies reveal that the phase diagram of the superfluid phases is substantially modified, altering the stability of the A and B phases as well as creating a new normal-to-superfluid transition even at zero temperature. The role of aerogel as a collection of impurities introduced into the superfluid will be explored by altering the density and correlations of the aerogel. The PIs will also study effects of other disordered porous media on the quantum phase diagrams. Experimental tools include NMR, heat capacity and ultrasound in addition to sound and torsional oscillator measurements to characterize the nature of the superfluid. The PIs will design new aerogels specifically tailored for studies of superfluid 3He and mixtures of 3He and 4He. Very low temperatures will in many instances be critical for the exploration of the phase diagram of pure 3He. %%% This Focused Research Group grant supports a comprehensive experimental and theoretical study of the effects of atomic-scale disorder on the nature of quantum-mechanical states, including superfluid states, which are preferred by liquid helium (isotopes of mass three and four atomic units) at temperatures close to absolute zero. Superfluids flow with no resistance from the surrounding medium or container. In the case of electron superfluids, i.e., superconductors such as lead below its transition temperature, this means electrical current flow with no resistance. Superfluid states a re found in nature in helium isotopes and electron systems at low temperatures, and are believed to taken on by neutrons in neutron stars. Superfluids permit classes of electronic devices called Superconducting Quantum Interference Devices (SQUID's) which are the world's most sensitive detectors of magnetic field. SQUID's are used in advanced medical practice in commercial electrocardiographs and magneto- encephalographs, which permit, respectively, non- invasive detection of heart and mental disorders. Superfluid helium put into rotation acts like a gyroscope: it has recently been demonstrated that such a gyroscope will allow detection of rotation at an unprecedented level of sensitivity. The research carried out under the present grant explores the effects of atom scale disorder on such superfluid states, and may have beneficial effects on technology involving sensor devices as mentioned, and more broadly, even to include present and future versions of microelectronic computer technology. ***

Parpia这项重点研究小组的拨款支持对纳米级无序对量子基态（包括超流体相）影响的全面实验和理论研究。发现3He和4He的混合物的相图在低密度气凝胶介质中发生了根本的变化，随后在气凝胶中进行了纯3He的研究。这些研究表明，超流相的相图发生了实质性的改变，改变了A相和B相的稳定性，甚至在零温度下也产生了新的正态到超流的转变。气凝胶作为杂质的集合引入超流体的作用将通过改变气凝胶的密度和相关性来探索。pi还将研究其他无序多孔介质对量子相图的影响。实验工具包括核磁共振、热容和超声波，以及声音和扭转振荡器测量，以表征超流体的性质。pi将设计新的气凝胶，专门用于研究超流体3He和3He和4He的混合物。在许多情况下，极低的温度对于探索纯3He的相图是至关重要的。这项重点研究小组的资助支持一项全面的实验和理论研究，研究原子尺度的无序对量子力学状态性质的影响，包括在接近绝对零度的温度下液态氦（质量为3和4原子单位的同位素）所偏爱的超流体状态。超流体流动时没有来自周围介质或容器的阻力。在电子超流体的情况下，即超导体，如铅低于其转变温度，这意味着电流无电阻流动。超流体状态存在于自然界的氦同位素和低温下的电子系统中，据信是由中子星中的中子产生的。超流体允许被称为超导量子干涉装置（SQUID）的电子设备的类别，它是世界上最敏感的磁场探测器。SQUID被用于商业心电图仪和脑电图仪的先进医疗实践中，它们分别允许对心脏和精神疾病进行非侵入性检测。旋转的超流氦就像一个陀螺仪：最近已经证明，这样的陀螺仪可以以前所未有的灵敏度检测到旋转。在本资助下进行的研究探索了原子尺度的无序对这种超流体状态的影响，并可能对涉及上述传感器设备的技术产生有益的影响，更广泛地说，甚至包括现在和未来的微电子计算机技术。＊＊＊