Materials Properties at Very Low Temperatures

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The work of the previous three years involving dynamic-pressure- dependent studies of collective modes in 3He, novel schemes to excite collective modes, sound propagation in UPt3, the development of a polarized 3He cell, sound propagation in oxide superconductors, the installation of a new-Oxford cryostat, and the superconducting properties of thin-film superlattices is summarized. Of particular importance was the characterization of an acoustic anomoly in the field dependence of the ultrasonic signal attenuation in UPt3 which may signal a new kind of phase transition. They propose continuing studies of the collective mode spectrum of 3He involving very short path lengths, novel excitation schemes, nonlinear effects, and the polarized liquid. The importance of microwave absorption studies in the dilution refrigerator region is noted and studies of UPt3 directed at the observation of collective modes are proposed. A top loading magnetometer alteration of our Oxford cryostat is proposed, again with the major emphasis on UPt3.