Helium-three and Helium-four at Very Low Temperatures

9630930爱德华兹氦同位素4He和3He分别形成玻色和费米子超流体。在超低温下，4He在3He中的溶解度很低，但最近的理论预测表明，在零温下，4He的溶解度是有限的。如果是这样的话，一种弱相互作用的稀玻色气体(溶解的4He准粒子)将共存于费米子超流体的溶液中，并为研究相互作用的超流体提供了一个独特的机会。溶解度的测定将导致对费米液体理论的严格检验。在相分离的液体混合物中，将测量两个共存相之间的界面自由能作为压力和温度的函数。结果将表明3He是否优先吸附在界面附近，并与基本的多体量子理论相比较。计划对两束氦原子束的会聚进行测量，以确定在极低速度下的散射截面的性质，并研究氦原子的二聚化。物质的基本理论，费米液体理论，用来理解像中子星、核物质和普通和超导金属中的电子这样截然不同的系统，将通过研究极低温度下溶解在液体3He中的4He原子来以一种新的方式进行测试。该实验是在绝对零度以上不到0.1度的温度下，测量4He原子在液体3He中扩散的速度，以及作为温度和压力的函数可以溶解的最大量。该理论预测了这些影响之间的关系。在第二个低温实验中，两束相互碰撞的4He原子束将被用来测量一对4He原子之间非常弱的化学键。***

w:\awards\awards96\*.doc 9630930 Edwards The helium isotopes 4He and 3He form Bose and Fermion superfluids respectively. The solubility of 4He in 3He is very low at ultra- low temperatures but recent theoretical predictions have suggested a finite value at zero temperature. If so, a weakly interacting dilute Bose gas (the dissolved 4He quasiparticles) would coexist in a solution of Fermion superfluid and provide a unique opportunity to study interacting superfluids. A stringent test of Fermi liquid theory will result from the determination of the solubility. The free energy of the interface between the two coexisting phases in phase-separated liquid mixtures will be measured as a function of pressure and temperature. The results will indicate whether 3He is preferentially adsorbed near the interface and compared to fundamental many-body quantum theories. A measurement of the coalescence of two helium atom beams is planned to determine the nature of the scattering cross-section at very low velocities and investigate the dimerization of helium atoms. %%% A fundamental theory of matter, Fermi liquid theory, used to understand systems as disparate as neutron stars, nuclear matter, and electrons in ordinary and superconducting metals, is to be tested in a new way by studying 4He atoms dissolved in liquid 3He at extremely low temperatures. The experiment is to measure, at temperatures less than 0.1 degrees above absolute zero, the rate at which the 4He atoms diffuse through the liquid 3He and the maximum amount that may be dissolved as functions of the temperature and pressure. The theory predicts a relation between these effects. In a second low temperature experiment, two beams of colliding 4He atoms will be used to measure the very weak chemical bond between a pair of 4He atoms. ***