Third Sound in Artificially Prepared Two-Dimensional Modulated Structures

调制结构中的波动现象不仅在固体物理学中引起普遍关注，而且在物理学中也引起普遍关注。最近波在随机介质中的局域化（安德森局域化）和准晶体的发现激发了人们对这些现象的兴趣。本研究的目的是阐明这些调制结构中的波的性质。在本实验中，第三声在二维准周期晶格彭罗斯晶格中的透射谱。与理论预期不同，传输对声的冲击方向敏感，频谱结构丰富。这是由于样本的有限性，因此结果与理论并不冲突。埃瓦尔德的构造表明，当结构因子的一个以上点位于同一个埃瓦尔德圆（三维球面）上时，传输被强烈抑制。这一事实表明，多重衍射在该系统中是重要的。首次观测到波在彭罗斯晶格中的透射谱。强调了彭罗斯晶格中多重衍射的重要性。在下一步的研究中，光谱必须在彭罗斯晶格以外的其他调制结构中测量，例如，随机晶格。

Wave phenomena in modulated structures are of general interest not only in the solid state physics but also in physics. Concurrent interests in the phenomena are stimulated by the recent discovery of localization of waves in random media (Anderson localization) and of quasicrystals. The aim of this research is to elucidate the nature of waves in these modulated structures.In the present experiment transmission spectra of third sound in the Penrose lattice which is a two-dimensional quasiperiodic lattice. Despite the theoretical expectation, the transmission is sensitive to the impinging direction of sound and the spectrum has rich structures. This is due to the finiteness of the sample and hence the result does not conflict with the theory.Ewald's construction suggests that the transmission is strongly suppressed when more than one spots of the structure factor locate on the same Ewald circle (sphere in three-dimensions). This fact implies that the multiple dffraction is important in this system.The transmission spectrum of waves in the Penrose lattice is observed for the first time. The importance of the multiple diffraction in the Penrose lattice is emphasized. In the next step of the research the spectra have to be measured in the other mudulated structures than the Penrose lattice, for example, the random lattice.