Shintani Hiroshi, Tanaka Hajime
Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Nat Mater. 2008 Nov;7(11):870-7. doi: 10.1038/nmat2293. Epub 2008 Oct 12.
The physical properties of a topologically disordered amorphous material (glass), such as heat capacity and thermal conductivity, are markedly different from those of its ordered crystalline counterpart. The understanding of these phenomena is a notoriously complex problem. One of the universal features of disordered glasses is the 'boson peak', which is observed in neutron and Raman scattering experiments. The boson peak is typically ascribed to an excess density of vibrational states. Here, we study the nature of the boson peak, using numerical simulations of several glass-forming systems. We discovered evidence suggestive of the equality of the boson peak frequency to the Ioffe-Regel limit for 'transverse' phonons, above which transverse phonons no longer propagate. Our results indicate a possibility that the origin of the boson peak is transverse vibrational modes associated with defective soft structures in the disordered state. Furthermore, we suggest a possible link between slow structural relaxation and fast boson peak dynamics in glass-forming systems.
拓扑无序的非晶态材料（玻璃）的物理性质，如热容量和热导率，与有序晶体材料的物理性质显著不同。理解这些现象是一个极其复杂的问题。无序玻璃的一个普遍特征是“玻色子峰”，这在中子和拉曼散射实验中可以观察到。玻色子峰通常归因于振动态的过剩密度。在这里，我们通过对几种玻璃形成系统的数值模拟来研究玻色子峰的本质。我们发现了证据，表明玻色子峰频率与“横向”声子的伊夫-雷格尔极限相等，超过该极限横向声子不再传播。我们的结果表明，玻色子峰的起源可能是与无序状态下有缺陷的软结构相关的横向振动模式。此外，我们提出了玻璃形成系统中缓慢结构弛豫与快速玻色子峰动力学之间的可能联系。
