Acquisition of a Compact Dilution Refrigerator

9317417 Lee这款紧凑型稀释式制冷机用于弗吉尼亚大学的实验，用于探索在极低温度下先进材料和新型固态结构的电子和电动力学响应。这些研究项目集中在相互作用电子系统的基本基态和基本激发性质的电子隧穿、噪声和输运研究。由于完全自旋、库仑和量子关联效应通常直到~0.1K的温度才变得明显，因此需要达到低于泵浦液体3H2(~0.3K)所能达到的温度，这就需要使用一种稀释制冷机，它可以快速而方便地达到大约0.02K的基温。预计稀释冰箱的正常使用将由三名主要研究人员负责：负责设施维护的主要用户李国章教授、潘永祥教授和陶以亚斯教授。Lee博士试图通过隧道效应和噪声实验来阐明在0.1K附近强相互作用区的可变距离跳跃(VRH)导体，如Si：P和PrBa2Cu3O7的基态。他还将使用稀释制冷机研究高迁移率超导体-半导体结构中低温下的大规模量子相干，以及新型超导体与正常金属之间的耦合如何深入了解可能的非传统超导机制。潘博士对完全由金属原子组成的高度有序的新材料感兴趣，这种材料由于不寻常的对称性而在低温下表现出半导体或绝缘行为，就像准晶或低维材料中出现的那样。对于这项工作，重要的是有能力系统地测量低至~0.03K的电阻率，以便确认和研究非金属行为的存在。Towe博士目前通过分子束外延生长高纯度半导体异质结。有效质量和迁移率的定量表征通常是通过测量Shubnikov-de Haas振荡和在极低温度下的霍尔效应量子化来完成的。Towe博士的研究将包括研究不同晶体取向的异质结构中的迁移率，以及氮化物半导体异质结构的发展。该仪器维护和操作简单，降温和样品周转时间相对较快，将成为研究生和本科生在固态和低温实验物理方面的优秀教学工具。稀释装置将安装在现有的4He杜瓦中，配备补偿的10T超导螺线管，并将与可运行的4He变温低温恒温器共享泵送和气体支持设施。***

9317417 Lee This compact dilution refrigerator used in experiments probing the electronic and electrodynamic response of advanced materials and novel solid-state structures at very low temperatures at University of Virginia. These research projects focus on electron tunneling, noise, and transport studies of the fundamental ground-state and elementary excitation properties of interacting electron systems. Because full spin, Coulomb, and quantum correlation effects often do not become manifest until temperatures of ~ 0.1K, attainment of temperatures below those achievable by pumped liquid 3H2(~0.3 K) will be required, making necessary the use of a dilution refrigerator which can achieve a base temperature of approximately 0.02K in a rapid and convenient manner. It is anticipated that normal use of the dilution refrigerator will be divided among three principal investigators: Prof. Mark Lee, who will be the principal user responsible for the maintenance of the facility, Prof. Joseph Poon, and Prof. Elias Towe. Dr. Lee seeks to elucidate aspects of the ground state in variable range hopping (VRH) conductors such as Si:P and PrBa2Cu3O7 in the strongly interacting regime around 0.1 K by tunneling and noise experiments. He will also use the dilution refrigerator to investigate large scale quantum coherency at low- temperature in high mobility superconductor-semiconductor structures, and how the coupling between novel superconductors and normal metals can shed insight into possibly unconventional superconducting mechanisms. Dr. Poon is interested in highly ordered new materials, composed entirely of metal atoms, that show semiconducting or insulating behavior at low temperature as a result of unusual symmetries, as occurs in quasicrystals, or low dimensionality. For this work it is important to have the ability to systematically measure resistivities down to ~ 0.03 K in a convenient manner in order to confirm and study the existence of non-metallic behavior. Dr. Towe currently grows high purity semiconductor heterostructures by molecular beam epitaxy. Quantitative characterization effective masses and mobilities is typically done by measuring Shubnikov-de Haas oscillations and of the Hall effect quantization at very low temperatures. Dr. Towe's investigation will include a study of mobilities in heterostructures of varying crystallographic orientation and development of nitride-based semiconductor heterostructures. This instrument is straightforward to maintain and operate, has a relatively rapid cool-down and sample turn- around time, and will thus serve as an excellent teaching tool for graduate and undergraduate students in solid-state and low- temperature experimental physics. The dilution unit will be housed in an existing 4He dewar equipped with a compensated 10 T superconducting solenoid and will share pumping and gas support facilities with an operational 4He variable temperature cryostat. ***