非晶材料中的声子-极化激元物理
Physics of Phonon-Polaritons in Amorphous Materials
摘要：
无序材料中玻色子激发的性质仍然难以捉摸，这是由于在无序存在下定义准粒子等关键概念的困难。我们报道了在玻璃中观测到的声子极化激元，包括玻色子峰（BP），即超过德拜定律的太赫兹模式。建立了一个基于扩散子概念的理论框架来模拟由于无序诱导散射而导致的极化激元线宽的加宽。结果表明，BP频率与线宽的扩散常数的标度与极化激元的Ioffe-Regel（IR）交叉频率密切相关。这一结果证明了BP在玻璃中集体玻色类激发的低能谱中的普遍性，远远超出了声学声子的传统情况，并建立了IR交叉作为BP背后的基本物理机制。
英文摘要：
The nature of bosonic excitations in disordered materials has remained elusive due to the difficulties in defining key concepts such as quasi-particles in the presence of disorder. We report on the experimental observation of phonon-polaritons in glasses, including a boson peak (BP), i.e. excess of THz modes over the Debye law. A theoretical framework based on the concept of diffusons is developed to model the broadening linewidth of the polariton due to disorder-induced scattering. It is shown that the scaling of the BP frequency with the diffusion constant of the linewidth strongly correlates with that of the Ioffe-Regel (IR) crossover frequency of the polariton. This result demonstrates the universality of the BP in the low-energy spectra of collective bosonic-like excitations in glasses, well beyond the traditional case of acoustic phonons, and establishes the IR crossover as the fundamental physical mechanism behind the BP.
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