Studies at Ultralow Temperatures

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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. ***