Elementary Excitations and Interactions in Bose Condensate State with Fermi particles

超流态4He是最典型的玻色凝聚态。在基于原子间相互作用阐明超流~4He性质的理论框架中，Feynman-Cohen导出的动力学结构因子从理论上讲是一个非常可靠的里程碑。然而，理论表达式与实验观测的动态结构因子之间存在较大的差异。而解释这种差异是超流体~4He最重要的问题之一。Ruvalds-Zawadowski的理论模型被认为是从Feynman-Cohen表达式中推导出可与实验定量比较的理论动态结构因子的既定理论。我们开始这个项目的目的是研究费米粒子在玻色凝聚系统中的行为。然而，在早期的研究中，我们发现一个重要的事实是，在外加压力升高时的两个子拉曼光谱并不适用于ruvalds-zawadow…。更多的KI模特。这一重要的发现使我们的实验集中于对纯超流~4He的两个子拉曼光谱的精确而详细的观测，以阐明元素激发之间相互作用的性质。为此，我们研制了一台3He低温恒温器激光光散射装置，它可以在0.65K、400 mW的激光输入下连续观察一周以上。文中还介绍了一种二维成像光子探测器，可以大大降低噪声，提高测量精度。利用所研制的实验装置，我们可以在0.65K的温度和0.45K的分辨率下观测到非常精确的双子拉曼光谱，压力值选择在SVP，5，10，15，20 kg/cm~2。在SVP下，观察到两个子峰的位置在5 kg/cm~2以上，而在Roton极小值时，两个子峰的位置是能量的两倍。随着压力的增加，正偏差增大。SVP处的光谱形状可以用传统的Ruvalds-Zawadoeski理论解释。然而，在5 kg/cm^2以上观察到的光谱形状不能用该理论解释。因此，我们可以断言，有必要发展新的理论来解释玻色凝聚态中基元激发之间的相互作用。较少

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