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Finite amplitude wave propagation in solid and liquid He 4

1980; American Physical Society; Volume: 21; Issue: 9 Linguagem: Inglês

10.1103/physrevb.21.3932

1095-3795

A. Hikata, H. Kwun, C. Elbaum,

High-pressure geophysics and materials

The amplitude response (i.e., relation between input and output amplitudes of a wave transmitted through a medium) of 10-MHz longitudinal wave is investigated in hcp and bcc solid $^{4}\mathrm{He}$ as well as normal fluid and superfluid $^{4}\mathrm{He}$. In all four phases the acoustic saturation in the amplitude response curve was observed. The results are well described by an equation for amplitude loss based on second-harmonic generation. The nonlinear parameter $\ensuremath{\beta}$ of these phases was evaluated. It is found that the magnitude $\ensuremath{\beta}$ in solid $^{4}\mathrm{He}$ is comparable to that of classical solids. Dislocation contributions to the amplitude response were also investigated and were ruled out as a significant source of the observed effects. It is concluded, therefore, that the large nonlinear amplitude response, which leads to saturation observed in solid $^{4}\mathrm{He}$ should be attributed to the unusually large compressibility, i.e., small elastic constants (second order), which, in turn, induces in solid $^{4}\mathrm{He}$ much larger strain amplitudes for a given applied stress than in ordinary solids.