Elementary Excitations and Interactions in Bose Condensate State with Fermi particles

超流^4He是最典型的玻色凝聚态。在以原子间相互作用为基础阐明^4He超流性质的理论框架中，费曼-科恩导出的动力学结构因子是一个非常可靠的理论里程碑。然而，理论表达式和实验观测的动态结构因子之间存在很大的差异。解释这种差异是超流体^4He的最重要的问题之一。Ruvalds-Zawadowski的理论模型被认为是一个建立的理论，从Feynman-Cohen表达式导出了一个理论上的动态结构因子，可以与实验定量地比较。我们开始这个项目的目的是研究玻色凝聚系统中费米粒子的行为。然而，在早期的研究中，我们发现了一个重要的事实，即在高压下的双共振拉曼光谱不符合Ruvalds-Zawadows公式 关于我们 ki模型。这一重要发现使我们的实验集中在对纯超流^4 He的双旋子拉曼光谱的精确详细观测上，以弄清基元激发之间相互作用的本质。为此，我们研制了一台^3He低温恒温器激光光散射仪，在400 mW激光输入下，可在0.65 K温度下进行一周以上的连续观测。本文还介绍了一种二维成像光子探测器，该探测器可以有效地降低噪声，提高测量精度。利用所研制的实验装置，我们可以在0.65 K的温度下，以0.45 K的分辨率，观测到非常精确的双旋拉曼光谱。压力值选择为svp、5、10、15、20 kg/cm ^2。在svp时，观察到双旋子峰的位置低于svp，而在svp时，观察到双旋子峰的位置高于5 kg/cm^2，而在旋子最小值时，双旋子峰的能量是svp的两倍。随着压力的增加，观察到正偏差增加。在svp处的光谱形状可以用传统的Ruvalds-Zawadoeski理论来解释。然而，在5 kg/cm ^2以上观测到的光谱形状不能用理论解释。因此，我们认为有必要发展新的理论来解释玻色凝聚态元激发之间的相互作用。少

Superfluid ^4He is the most typical Bose-condensed state. In the theoretical framework to clarify the properties of superfluid ^4He based on interatomic interactions, the dynamic structure factor derived by Feynman-Cohen is a very reliable mile-stone from a theoretical view point. However there is considerable difference between the theoretical expression and the experimentally observed dynamic structure factor. And to explain the difference is one of the most important problems of superfluid ^4He. The theoretical model by Ruvalds-Zawadowski has been regarded as an established theory to derive a theoretical dynamic structure factor, that can be quantitavely compared with experiments, from the Feynman-Cohen expression. We started this project with the purpose to investigate behavior of Fermi-particles in the Bose-condensed system. However, in the early research, we found an important fact that the two-roton Raman spectrum at elevated applied pressure does not fit to the Ruvalds-Zawadows … More ki model. The important finding made us concentrate our experiments on the precise detailed observation of two-roton Raman spectra of pure superfluid ^4He, to clarity the nature of interactions between elementary excitations. For that purpose, we developed a ^3He cryostat laser light scattering, with which we could make continuous observation over one week at 0.65 K with 400 mW laser imput. A 2-dimensional imaging photon detector was also introduced, with which we could reduce noises and increase accuracy considerably. With the experimental apparatus thus developed, we could observe very accurate two-roton Raman spectra at a temperature of 0.65 K with a resolution of 0.45 K. The pressure values were chosen at svp, 5, 10, 15, 20 kg/cm^2. The position of the two-roton peak was observed below at svp and above over 5 kg/cm^2 compared with twice the energy at roton minimum. The positive deviation was observed increase as the pressure increased. The spectral shape at svp can be explained by the conventional Ruvalds-Zawadoeski theory. However, the spectral shape observed over 5 kg/cm^2 connot be explained by the theory. We could thus claim necessity of development of new theories to interpret interacations between elementary excitations in Bose-condensed state. Less