低温下固体$^4$ He中的低频声学
Low frequency acoustics in solid $^4$He at low temperature
摘要：
用低频（20 Hz ~ 20 kHz）高灵敏度声换能器研究了六方晶系$^4$ He样品的弹性性质。与其他研究者的发现一致，研究的大多数样品在低温下变得非常显著地更硬;观察到泊松比$ν$从低于20 mK时的0.28增加到0.7 K时的$\sim 0.35$。$ν$的变化范围因样品而异，具体取决于样品的热历史和机械历史。在熔化曲线上仔细生长的晶体显示出不同的行为，$ν$的变化发生在较低的$T$下，并且更突然。
英文摘要：
The elastic properties of hcp $^4$He samples have been investigated using low frequency (20 Hz to 20 kHz) high sensitivity sound transducers. In agreement with the findings of other workers, most samples studied grew very significantly stiffer at low temperature; Poisson's ratio $ν$ was observed to increase from 0.28 below 20 mK to $\sim 0.35$ at 0.7 K. The span of the variation of $ν$ varies from sample to sample according to their thermal and mechanical history. Crystals carefully grown at the melting curve show a different behavior, the change in $ν$ taking place at lower $T$ and being more abrupt.
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