Weak Links and Proximity Effects in Microstructures of He-4

*非技术摘要*这个低温物理项目的目标是了解正在经历相变的系统如何受到附近正在经历相同相变的系统的影响。这就是所谓的“接近”效应。问题是，这些系统必须有多近才能相互影响。原子相互作用的细节通常被认为是回答这样一个问题的答案，但它并不相关，因为在相变附近，发生的长程波动发生的长度远远大于单个原子之间的距离。这些涨落支配着系统的热力学行为。这项研究的重点是液氦在其超流体转变附近，作为许多其他系统的一般行为的范例。这些实验将研究相对较大的液体区域，这些液体与不同尺寸的小通道相连。这些研究将类似于对由弱势垒隔开的超导体阵列的研究。从事该项目的学生和博士后研究人员将接受硅片加工、直接晶片键合、各种诊断技术和高分辨率低温测量方面的培训。这为他们在学术界、工业界和政府实验室的工作安排做好了准备。*技术摘要*这个低温物理研究项目将通过不同强度的链接解决与一系列超流体区域耦合相关的问题。这将通过在硅片上光刻形成一系列与纳米通道相连的盒子来实现。将测量该阵列的热容和超流体分数。通道的纵横比将被系统地改变，以改变耦合。正在讨论的物理类似于由纳米桥连接的超导体和通过弱势耦合的玻色凝聚体。这项拟议的工作与这些工作的不同之处在于，研究将在超流体转变附近的区域进行，在那里涨落主导热力学响应。这项工作将有助于更好地理解薄弱环节的概念以及波动在这种耦合中所起的作用。这项工作的性能将涉及硅光刻；直接晶片键合；使用原子力显微镜、电子显微镜和光学干涉法进行诊断；以及最终的高分辨率低温测量。学生和博士后研究人员将接受与学术界、工业和政府实验室的职业相关的各种实验技术培训。

*****NON-TECHNICAL ABSTRACT*****This low temperature physics project has the goal of understanding how a system undergoing a phase transformation can be influenced by a nearby system undergoing the same transformation. This is referred to as a "proximity" effect. The question is how close such systems have to be to influence each other. The details of the atomic interactions, which normally would be considered to answer such a question, are not relevant because near a phase transition there are long-range fluctuations that take place over lengths much larger than the distance between individual atoms. These fluctuations dominate the thermodynamic behavior of the system. This study focuses on liquid helium near its superfluid transition as a paradigm of what is expected to be a general behavior of many other systems. The experiments will study relatively large regions of liquid linked with small channels of various dimensions. These studies will be analogous to studies of arrays of superconductors separated by weak barriers. Students and postdoctoral researchers working on this project will be trained in silicon wafer processing, direct wafer bonding, a variety of diagnostic techniques, and high-resolution low temperature measurements. This prepares them for job placements in academia, industry and government laboratories.***** TECHNICAL ABSTRACT*****This low temperature physics research project will address issues associated with the coupling of an array of superfluid regions via links of various strength. This will be done by forming lithographically on a silicon wafer an array of boxes that are linked with nanometer channels. The heat capacity of this array and the superfluid fraction will be measured. The aspect ratios of the channels will be varied systematically to modify the coupling. The physics being addressed is similar to that of superconductors linked by nanobridges and of Bose condensates coupled through a weak potential. The proposed work differs from these in that the studies will be done in the region near the superfluid transition where fluctuations dominate the thermodynamic response. The work will lead to a better understanding of the concept of weak links and the role that fluctuations play in this coupling. The performance of this work will involve silicon lithography; direct wafer bonding; diagnostics using atomic force microscopy, electron microscopy and optical interferometry; and, ultimately high resolution low temperature measurements. Students and postdoctoral researchers will be trained in a variety of experimental techniques relevant to careers in academia, industry and government laboratories.