Flenner Elijah, Szamel Grzegorz
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
J Phys Chem B. 2025 Feb 13;129(6):1855-1863. doi: 10.1021/acs.jpcb.4c07545. Epub 2025 Feb 4.
Two nearly universal and anomalous properties of glasses, the peak in the specific heat and plateau of the thermal conductivity, occur around the same temperature. This coincidence suggests that the two phenomena are related. Both effects can be rationalized by assuming Rayleigh scaling of sound attenuation and this scaling leads one to consider scattering from defects. Identifying defects in glasses, which are inherently disordered, is a long-standing problem that was approached in several ways. We examine candidates for defects in glasses that represent areas of strong sound damping. We show that some defects are associated with quasi-localized excitations, which may be associated with modes in excess of the Debye theory. We also examine generalized Debye relations, which relate sound damping and the speed of sound to excess modes. We derive a generalized Debye relation that does not resort to an approximation used by previous authors. We find that our relation and the relation given by previous authors are almost identical at small frequencies and also reproduce the independently determined density of states. However, the different generalized Debye relations do not agree around the boson peak. While generalized Debye relations accurately predict the boson peak in two-dimensional glasses, they underestimate the boson peak in three-dimensional glasses.
玻璃的两个几乎普遍存在且异常的性质，即比热峰值和热导率平台，出现在大致相同的温度附近。这种巧合表明这两种现象是相关的。通过假设声衰减的瑞利标度，可以使这两种效应合理化，并且这种标度促使人们考虑来自缺陷的散射。识别本质上无序的玻璃中的缺陷是一个长期存在的问题，人们通过多种方式来解决。我们研究了玻璃中代表强声阻尼区域的缺陷候选者。我们表明，一些缺陷与准局域激发有关，这可能与超出德拜理论的模式有关。我们还研究了广义德拜关系，它将声阻尼和声速与多余模式联系起来。我们推导了一个不采用先前作者所使用近似方法的广义德拜关系。我们发现，我们的关系与先前作者给出的关系在小频率下几乎相同，并能重现独立确定的态密度。然而，不同的广义德拜关系在玻色子峰附近并不一致。虽然广义德拜关系能准确预测二维玻璃中的玻色子峰，但它们低估了三维玻璃中的玻色子峰。
