非晶态固体氦的激发
Excitations of amorphous solid helium
摘要：
我们提出了中子散射测量的动态结构因子，$S(Q,ω)$，非晶态固体氦限制在47 $Å$孔径MCM-41在压力48.6巴。在低温下，$T$ = 0.05 K，我们观察到的限制量子非晶态固体和MCM-41粉末颗粒之间的块状多晶固体的$S(Q,ω)$。没有观察到类似液体的声子-声子模式，在低能量（$ω<$ 1.0 meV）或量子非晶态固体特有的模式，可能表明超流的其他明确定义的模式。相反，受限非晶和块状多晶固体的$S(Q,ω)$似乎非常相似。在较高温度（$T>$ 1 K）下，MCM-41孔中的非晶态固体熔化成液体，该液体具有在压力下正常液体$^4$ He的特征的接近$ω\simeq$ 0的宽$S(Q,ω)$峰值。给出并比较了非晶和多晶固态氦的$S(Q,ω)$表达式。在以前的测量液体$^4$他限制在MCM-41中在较低的压力下，在液体旋子模式的强度随着压力的增加而减小，直到旋子消失在固化压力（38巴），与没有旋子在这里观察到的固体一致。
英文摘要：
We present neutron scattering measurements of the dynamic structure factor, $S(Q,ω)$, of amorphous solid helium confined in 47 $Å$ pore diameter MCM-41 at pressure 48.6 bar. At low temperature, $T$ = 0.05 K, we observe $S(Q,ω)$ of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquid-like phonon-roton modes, other sharply defined modes at low energy ($ω<$ 1.0 meV) or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather the $S(Q,ω)$ of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature ($T>$ 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad $S(Q,ω)$ peaked near $ω\simeq$ 0 characteristic of normal liquid $^4$He under pressure. Expressions for the $S(Q,ω)$ of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid $^4$He confined in MCM-41 at lower pressure the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here.
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