ULTRASONIC STUDIES OF SOME POLYMERS AT LOW TEMPERATURES

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Abstract
The sound velocity and acoustic absorption have been measured in polymethylmethacrylate (PMMA), polyethylmethacrylate (PEMA), and polycarbonate (PC) from 60mK to 10K. For all three polymers similar acoustic properties are observed. At low temperatures, in contrast to earlier measurements, we find an absorption proportional to ω0T3 and a logarithmic variation of the sound velocity, as expected from the tunneling model. At higher temperature the absorption reaches a plateau. This is for the first time the plateau, predicted in the tunneling model, has been observed in an amorphous material

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