亚稳态hcp固态氦在低于熔化压力下的研究
Investigating metastable hcp solid helium below its melting pressure
摘要：
我们首次尝试在低于熔化压力下制备亚稳态的六方晶系固态氦。聚焦声脉冲沿单畴六方晶系氦-4晶体的c轴发射，从刚高于熔化压力的静压开始。声音脉冲尽可能简单，只有一个负的和一个正的摆动。通过光学干涉测量方法监测焦点处的密度。进行的数值模拟表明，晶体各向异性分裂成两个单独的脉冲，对应于沿c轴的纵波和径向一个垂直于它的聚焦的放大因子仍然是重要的。产生的负压波动高达0.9 bar，超过了静态熔化压力极限。提出了在检测方法和聚焦放大方面的改进。
英文摘要：
We report a first attempt to produce metastable hcp solid helium below its melting pressure. A focused sound pulse is emitted along the c-axis of a mono-domain hcp helium-4 crystal starting from a static pressure just above the melting pressure. The sound pulse is made as simple as possible with one negative and one positive swing only. Density at focus is monitored by an optical interferometric method. Performed numerical simulations show that the crystal anisotropy splits the focused wave into two separate pulses, corresponding to a longitudinal wave along the c-axis and a radial one perpendicular to it. The amplification factor due to focusing remains nevertheless important. Negative pressure swings up to 0.9 bar have been produced, crossing the static melting pressure limit. Improvements in the detection method and in the focusing amplification are proposed.
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