玻璃的低温特性:双能级系统、软模式和光谱扩散

R. Silbey, A. Heuer, D. Dab
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引用次数: 0

摘要

提出了一种系统地发现玻璃中隧穿系统的理论方法,并对Phillips、Anderson、Halperin和Varma的标准隧穿模型进行了微观论证。计算表明,隧道模型的主要假设在定性上是正确的;然而,隧道参数的分布函数存在较小的偏差,使得比热符合T1+ε定律,导热系数符合T2-α定律。计算还允许定量估计两个能级系统与声子的相互作用(变形势)。与最近的猜想相反,计算证实了弱耦合的情况。然后通过Lennard-Jones模型将该理论映射到所有结构玻璃上,该模型用于玻璃中子单元之间的相互作用。这些亚单位是分子系统(例如,聚合物玻璃中的单体或硅酸盐玻璃中的四面体)。从这个映射,我们发现隧道参数,从而热性能,大多数结构玻璃可以半定量估计从微观参数的哈密顿量。进一步的论证允许绘制隧道参数与宏观实验特性(声速和密度)之间的联系。计算也顺利地进入了“软势”模型,该模型解释了在更高温度(~10K)下的热行为,从而提供了一个通用模型。根据这些计算,可以计算出引起光谱扩散的隧穿速率的分布,并与最近的实验进行比较。这些将在会议上提出,以及在玻璃中引入杂质(即发色团)对两能级系统分布的影响的计算。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Low Temperature Properties of Glasses: Two Level Systems, Soft Modes, and Spectral Diffusion
A theoretical method that systematically finds tunneling systems in glasses and allows a microscopic justification of the standard tunneling model of Phillips and Anderson, Halperin and Varma is presented. The calculation shows that the major assumptions of the tunneling model are qualitatively correct; however, there are small deviations in the distribution functions of tunneling parameters that give rise to the T1+ε law for specific heat and the T2-α law for the thermal conductivity. The calculation also allows a quantitative estimate of the interaction of the two level systems with phonons (the deformation potential). The calculations confirm the weak coupling picture, in contrast with recent conjectures. The theory is then mapped onto all structural glasses via a Lennard-Jones model for the interaction between sub-units in the glass. These sub-units are molecular systems (e.g monomers in a polymer glass or tetrahedra in silicate glasses). From this mapping, we find that the tunneling parameters, and hence the thermal properties, of most structural glasses can be estimated semi-quantitatively from the microscopic parameters of the Hamiltonian. A further argument allows the connection between the tunneling parameters and the macroscopic experimental properties (sound velocity and density) to be drawn. The calculations also go smoothly into the "soft potential" model that explains the thermal behavior at higher temperatures (~10K), thus providing a universal model. From these calculations, the distribution of tunneling rates that give rise to spectral diffusion can be calculated and compared to recent experiments. These will be presented at the conference, along with calculations of the effect on the two level system distributions of introducing an impurity (i.e. chromophore) into the glass.
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