Studies with Liquid Helium Films

这个低温物理项目研究氦薄膜的独特性质。令人感兴趣的是薄膜的基本行为及其在凝聚态物理中感兴趣的问题的其他研究中的应用。我们将研究He-3/He-4混合膜系统的新方面，包括局域化、在氢衬底上的测量、二维费米液体参数的确定以及在极低温度下在He-4膜上的二维He-3中寻找新的超流状态。这项工作探索了多孔材料中氦的毛细凝结和雪崩现象，并检验了当前理论概念与此类系统的相关性。在一维和二维的图案化衬底上进行了氦薄膜的实验，重点是二维局域化。这些方法包括核磁共振、石英晶体微天平共振、He-4和He-3/He-4混合薄膜热性质的三次声学和热容研究，以及多孔材料中毛细凝结和雪崩事件的高分辨率电容测量。除了有助于理解氦膜本身的行为之外，这项工作还与费米系统、局域化、二维相变、雪崩现象和毛细凝聚等领域的更广泛的社区相关。它还为研究生提供了极好的培训，为与之相关的本科生提供了参与研究的机会。%本研究调查了液氦的显着性质。这种研究提供了对自然的独特见解，这是任何其他物质的研究都无法获得的。氦薄膜提供了有关氢等弱结合表面行为的信息，这有助于理解表面润湿的一般问题。对经过刻意图案化处理的表面上的这种薄膜的波动特性进行研究，可以更好地理解波是如何被困在新环境中的。对这两种自然存在的氦的薄膜混合物的研究可能会导致一种令人兴奋的新超流体的发现，这种超流体是预测的，但尚未被观测到。氦在其无摩擦的超流状态下被用来进一步理解当氦从海绵物质中排出时观察到的戏剧性雪崩行为。这些实验可以更好地理解从多孔材料中去除流体的过程。参与这项工作的学生可以使用复杂的仪器为他们提供高质量的实践研究体验。

9819122HallockThis low temperature physics project investigates the unique properties of helium films. Of interest are the fundamental behavior of the films and their application in other studies of problems of interest in Condensed Matter Physics. New aspects of the He-3/He-4 mixture film system, including localization, measurements on hydrogen substrates, the determination of two dimensional Fermi liquid parameters, and the search for a new superfluid state in the two dimensional He-3 atop a He-4 film at very low temperatures will be investigated. The work explores capillary condensation and avalanche phenomena with helium in porous materials, and examines the relevance of current theoretical notions to such systems. Experiments are conducted with helium films on patterned substrates in one and two dimensions, with a focus on two dimensional localization. The methods include NMR, quartz crystal microbalance resonance, third sound, and heat capacity studies of the thermal properties of He-4 and He-3/He-4 mixture films, and high resolution capacitance measurements of capillary condensation and avalanche events in porous materials. In addition to contributing to progress in understanding the behavior of helium films themselves, the work has relevance to the wider community in the areas of Fermi systems, localization, two dimensional phase transitions, avalanche phenomena, and capillary condensation. It also provides excellent training for the graduate students and research participation opportunities for the undergraduates who are associated with it.%%%This research investigates the remarkable properties of liquid helium. Such study provides unique insights into nature which are not available by the study of any other substance. Thin films of helium provide information on the behavior of weak binding surfaces such as hydrogen, which aids in the understanding of the general problem of wetting of surfaces. Study of the wave character of such thin films on surfaces which have been deliberately patterned allows an enhanced understanding of how waves can be trapped in novel environments. The study of thin film mixtures of the two naturally occurring forms of helium may result in the discovery of an exciting new kind of superfluid which is predicted but has not yet been observed. Helium in its friction-free superfluid state is utilized to further understand the dramatic avalanche behavior observed when helium drains from spongy substances. These experiments allow a better understanding of the process of fluid removal from porous materials. Students involved in this work are provided with a high quality hands-on research experience using sophisticated instrumentation.