Studies at Ultralow Temperatures

超低温研究

• 批准号: 9973255
• 负责人: Hans Bozler
• 金额: $ 40.5万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-06-01 至 2003-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9973255&HistoricalAwards=false
• 关键词: Studies; Ultralow; Temperatures

9973255BozlerThis is a condensed matter physics project that focuses on superfluid He-3, 2D magnetism of He-3, and a novel technique for absolute thermometry at ultralow temperatures. The results of magnetization measurements in the superfluid He-3 phases are inconsistent and depend on whether the measurements are performed with a SQUID or by NMR. The missing physics represents a significant challenge. Recent experiments measure the absolute magnetization of normal and superfluid He-3 using a SQUID and displacement technique. Continued work on the superfluid phases of He-3 includes studies of the A-B interface and the high field phase diagram of He-3 in restricted geometries such as aerogel. Thin films of He-3 exhibit two-dimensional magnetism which can be studied by NMR. These studies feature an NMR technique at very low applied field using a SQUID as the sensor. Early experiments are at ferromagnetic coverages. Extensions of this work to both higher coverages and single monolayer coverages are planned. We are developing an advanced DC SQUID system in collaboration with TRW. The SQUID is capable of following signals at much higher frequencies and slew rates than commercially available systems, and is used for a proposed method of absolute primary thermometry. Graduate students participating in the project benefit from exposure to exciting fundamental physics research and experience with state-of-the-art instrumentation. The provides excellent training for a wide range of careers. %%%This is a condensed matter physics study of materials at ultralow temperatures, together with the development of ultralow temperature techniques. Most of this work takes place at temperatures well below 1 K, and much of it is at temperatures below 1 mK. The USC Ultralow Temperature Laboratory is equipped to attain low temperatures and to make precision, low noise, and very low power measurements. Experiments focus on the study of the superfluid phases of He-3, the magnetism of two-dimensional films of He-3, and new techniques to measure the absolute temperature at milliKelvin temperatures. The experiments in this project are important to the fundamental understanding of the superfluid phases of He-3 which is an important model system for many phenomena in condensed matter. The properties of the two-dimensional films provide an excellent laboratory for the study of two-dimensional magnetism because the interactions can be greatly varied by small changes in density, allowing us to test theories of two-dimensional phase order in a systematic way. The ability to measure temperatures in the milliKelvin range is still limited, with several very good relative thermometers, but no absolute thermometer. The project uses the frequency spectrum of thermal fluctuations to determine the absolute temperature. Graduate students participating in the project benefit from exposure to exciting fundamental physics research and experience with state-of-the-art instrumentation. The provides excellent training for a wide range of careers. ***

这是一个凝聚态物理项目，主要研究超流体He-3， He-3的二维磁性，以及超低温下绝对测温的新技术。超流体He-3相的磁化测量结果不一致，这取决于测量是用SQUID还是用NMR进行的。缺失的物理现象是一个重大挑战。最近的实验使用SQUID和置换技术测量了正常和超流体He-3的绝对磁化强度。对He-3超流体相的持续研究包括对A-B界面和He-3在气凝胶等受限几何结构中的高场相图的研究。He-3薄膜具有二维磁性，可通过核磁共振进行研究。这些研究的特点是核磁共振技术在非常低的应用领域，使用鱿鱼作为传感器。早期的实验是在铁磁覆盖下进行的。计划将这项工作扩展到更高的覆盖范围和单层覆盖范围。我们正在与TRW合作开发先进的直流SQUID系统。SQUID能够以比商用系统高得多的频率和转换率跟踪信号，并用于拟议的绝对初级测温方法。参与该项目的研究生可以接触到令人兴奋的基础物理研究并体验最先进的仪器。它为各种各样的职业提供了优秀的培训。这是一个凝聚态物理研究材料在超低温下，连同超低温技术的发展。大部分工作都是在远低于1 K的温度下进行的，其中大部分温度低于1 mK。南加州大学超低温实验室配备了低温设备，可以进行精确、低噪音和极低功耗的测量。实验重点研究了氦-3的超流体相，氦-3二维膜的磁性，以及在毫开尔文温度下测量绝对温度的新技术。氦-3是凝聚态中许多现象的重要模型系统，本项目的实验对于从根本上认识氦-3的超流相具有重要意义。二维薄膜的性质为二维磁性研究提供了一个很好的实验室，因为密度的微小变化可以极大地改变相互作用，使我们能够以系统的方式测试二维相顺序理论。测量毫开尔文范围内温度的能力仍然有限，有几种非常好的相对温度计，但没有绝对温度计。该项目利用热波动的频谱来确定绝对温度。参与该项目的研究生可以接触到令人兴奋的基础物理研究并体验最先进的仪器。它为各种各样的职业提供了优秀的培训。＊＊＊