Applications of the Ordered Phases of Helium Three to Broader Questions in Physics

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9971694OsheroffThis is a low temperature physics project dealing with less abundant isotope of helium, He-3. The low temperature ordered phases of solid and liquid He-3 exhibit complex yet remarkably well understood and easily measured physical properties which in many instances mimic the behavior seen less clearly in systems with much greater technological importance. For instance, one can easily observe antiferromagnetic domain walls in the U2D2 spin ordered phase of solid He-3 from shifts in the NMR spectra of the adjacent magnetic domains. This ability will be utilized in the present research program to study domain wall pinning and mobility in an antiferromagnet cleanly for the first time. This knowledge should be useful in understanding the stability of magnetic systems on a mesoscopic scale, and macroscopic tunneling phenomena generally. In another example, the p-wave 3He BCS superfluid ground state would be infinitely degenerate at Tc were it not for critical fluctuations, which are predicted to stabilize phases near Tc which are different from those seen at lower temperatures. This research program will probe the width of this region, and attempt to identify the ordered phases near Tc, thus providing a new test of our understanding of the theory of critical phenomena. The project educates primarily graduate students, although physics majors carry out senior honors projects in the lab as well. Students who pursue low temperature studies obtain a rigorous and very broad education in condensed matter physics and experimental techniques. %%%This low temperature physics project will utilize many of the unique properties of the low temperature phases of solid and liquid He-3 to study specific properties of these ordered phases whose physical origins are common to properties seen in other more technologically important materials, such as those used in magnetic memory devices. In one set of experiments, the nature and mobility of the boundaries between magnetically ordered domains with different orientations will be studied in a magnetically ordered phase of solid 3He using magnetic resonance techniques. This study will bear on the question of how a system can quantum mechanically tunnel through a barrier which is too high for it to go over. A second study will involve superfluid 3He, which exhibits ordered phases similar to those seen in conventional superconductors, but much more complex. The nature of the superfluidity just below the transition to the ordered state will be used in a novel test of the theory which appears to successfully describe all second order, or 'continuous' phase transitions. This will provide a unique test of the applicability and validity of this Nobel prize winning theory. The project educates primarily graduate students, although physics majors carry out senior honors projects in the lab as well. Students who pursue low temperature studies obtain a rigorous and very broad education in condensed matter physics and experimental techniques. ***