Anomalous nonlinear attenuation of ultrasound in solid 4He in a torsional oscillator below 200 mK

27th International Conference on Low Temperature Physics

Iwasa, I.^1 ; Goodkind, J.M.^2 ; Kojima, H.^3

Department of Mathematics and Physics, Kanagawa University, Kanagawa

259-1293, Japan^1

Physics Department, University of California, San Diego

CA

92093, United States^2

Serin Physics Laboratory, Rutgers University, NJ

08854, United States^3

关键词: Amplitude dependence;    Nonlinear attenuation;    Simultaneous measurement;    Spatial variations;    Torsional oscillation;    Torsional oscillator;    Ultra low temperatures;    Velocity changes;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/568/1/012005/pdf
DOI  :  10.1088/1742-6596/568/1/012005

来源: IOP

【 摘 要 】

In order to elucidate the ultra-low temperature behavior of solid4He, simultaneous measurements of longitudinal ultrasound (US) and torsional oscillation have been made. Changes in attenuation and velocity of US at 10 MHz have been measured in polycrystalline hcp4He samples (0.3 or 20 ppm of3He impurity) grown in a 1 kHz torsional oscillator (TO). In a 0.3 ppm3He sample, the US attenuation and velocity were found to depend on the US drive voltage at temperatures below 70 mK where the anomalies in the TO frequency and dissipation were also observed. The US attenuation at low T (10 mK) decreased monotonically as the drive voltage was decreased but then remained small and constant as the drive voltage was increased again. The US velocity change at low T was negative with respect to the high-T (400 mK) value, contrary to the positive sign expected from the known variation in the shear modulus. In a 20 ppm3He sample, both the US and TO anomalies shifted to 150 mK. The amplitude dependence and hysteresis of US attenuation were related to pinning of dislocations by3He impurities, and nonlinear spatial variations of the amplitude of US pulses were derived.