STUDY OF PHONON TRANSMISSION AT THE SOLID AND LIQUID INTERFACE OF ^3He

设计并制作了能在35个大气压的^3He熔化压力下穿孔的声室。ZnO被用作声波单元中的换能器。为了提高对^3He的传输效率，在换能器和^3He之间溅射了双层减反射膜。首先，我们在400MHz的频率下，观察到零声在液态^3He中的传播。这是第一次在400MHz的高频下观察到零声。在2mK温度范围内，声量子具有比热激发能量更高的能量，使得声量子的吸收发生在准粒子的碰撞中。根据朗道Ferimi液体理论，在该区域中的吸收与频率的平方成比例，并且与温度无关。从我们的实验结果来看，吸收在绝对零度下保持有限。我们估计可以观测到零声吸收的量子极限，作为对我们系统的一个测试，我们观测了固体^4He中的声传播。在低功率区，声信号在固体^4He中的传播随输入声功率的增大而增大。当声功率增加时，发生非线性吸收，声信号在固体^4He中的传播达到饱和。这一事实证实了我们的系统有足够的灵敏度和功率来观察固体He中的声传播。我们曾试图在我们的细胞中制造换能器之间的固体和液体界面，但很难控制和稳定界面。通过界面传播或在界面反射的声波信号，至今未能观测到。

The sonic cell was designed and made, which bore under the ^3He melting pressure of 35 atm. ZnO is used as the transducer in the sonic cell. In order to increase transmission efficiency into ^3He, double layred anti-reflection coating is sputtered between the transducer and ^3He.First, we observed the propagation of zero sound in liquid ^3He down to temperature of about 2 mK at a frequency of 400MHz. This is the first observation of zero sound at the high frequency of 400MHz. In the 2mK temperature regime, the sound quanta has higher energy than thermal excitation energy so that the absorption of sound quanta takes place in the collisions of quasiparticles. According to Landau Ferimi liquid theory, the absorption in this regime is proportional to the square of frequency and independent of temperature. From our experimental result, the absorption is seen to remain finite at absolute zero temperature. The quantum limit of zero sound absorption is estimated to be observed.We observed sound propagation in solid ^4He as a test of our system. The sound signal propagating through solid ^4He increased inearly with input sound power in the low power regime. when the sound power was increased, nonlinear absorption occurred and the sound signal propagating through solid ^4He was saturated. This fact confirmed that ur system had enough sensitivity and power to observe sound propaation through solid He.We have tried to make solid and liquid interface between the transducer in our cell but it was hard to control and stabilize the interface. It has not been succeed to observe the sund signal which ropagates through or is reflected at the interface.