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

w：\awards\awards96\num.doc 9705295 Parpia 这个重点研究小组资助支持对纳米级无序对量子基态（包括超流相）的影响进行全面的实验和理论研究。 发现3He和4He的混合物的相图被低密度气凝胶介质彻底改变后，气凝胶中纯3He的研究迅速跟进。这些研究表明，超流相的相图被大幅修改，改变了A和B相的稳定性，甚至在零温度下也产生了新的正常到超流的转变。 将通过改变气凝胶的密度和相关性来探索气凝胶作为引入超流体的杂质集合的作用。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 除了声音和扭转 振荡器测量来表征超流体的性质。 PI将设计专门用于超流3He以及3He和4He混合物研究的新型气凝胶。在许多情况下，非常低的温度对于探索纯3He的相图是至关重要的。 这个重点研究小组资助支持一个全面的实验和理论研究的影响，原子尺度的无序的性质，量子力学状态，包括超流体 国家， 其优选地由液体 氦（质量为3和4原子单位的同位素），温度接近绝对零度。超流体的流动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， 当超导体如铅的温度低于其转变温度时，这意味着电流流动没有电阻。超流体状态在自然界中的氦同位素和电子系统中在低温下被发现，并且被认为是由中子星中的中子呈现的。 超流体允许称为超导量子干涉器件（SQUID）的电子设备，这是世界上最灵敏的磁场探测器。 SQUID在先进的医疗实践中用于商业心电图仪和磁共振成像仪。 脑电图仪，分别允许， 心脏和精神疾病的非侵入性检测。 投入旋转的超流氦就像一个陀螺仪：最近已经证明，这样的陀螺仪将允许以前所未有的灵敏度检测旋转。在本基金下进行的研究探索了原子尺度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影响，更广泛地说，甚至包括微电子计算机技术的当前和未来版本。 ***

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. ***