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arXiv 1701.05041cond-mat.softcond-mat.dis-nncond-mat.mtrl-scicond-mat.othercond-mat.stat-mech
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玻色子峰模与玻璃介电$α$弛豫的直接联系

Direct link between boson-peak modes and dielectric $α$-relaxation in glasses

B. Cui, R. Milkus, A. Zaccone

摘要:

我们计算的介电响应的玻璃开始从微观系统浴哈密顿的Zwanzig-Caldeira-Leggett型,并使用从动力学理论的记忆功能在所得的广义Langevin方程中的一个anasterian。由此产生的框架需要的振动态密度(DOS)的知识作为输入,我们从数值评估的边缘稳定的谐波无序晶格,具有较强的玻色子峰(超过德拜$\simω_{p}^{2}$法的软模式过剩)。基于此计算的介电函数与实验数据相比,甘油在$T\lesssim T_{g}$的范例情况下。良好的协议被发现的反应(实部)的响应和$α$ -松弛峰的虚部,与早期的理论方法,特别是在反应模量的显着改善。在$α$峰的低频侧,拟合支持在消失的本征频率处存在$\sim ω_{p}^{4}$模式,如最近在[Phys.Rev.Lett. 117,035501(2016)]。我们的框架恢复了$α$ -翼不对称性和拉伸指数行为,这表明这些特征在很大程度上是由DOS中的软玻色子峰模引起的。

英文摘要:

We compute the dielectric response of glasses starting from a microscopic system-bath Hamiltonian of the Zwanzig-Caldeira-Leggett type and using an ansatz from kinetic theory for the memory function in the resulting Generalized Langevin Equation. The resulting framework requires the knowledge of the vibrational density of states (DOS) as input, that we take from numerical evaluation of a marginally-stable harmonic disordered lattice, featuring a strong boson peak (excess of soft modes over Debye $\simω_{p}^{2}$ law). The dielectric function calculated based on this ansatz is compared with experimental data for the paradigmatic case of glycerol at $T\lesssim T_{g}$. Good agreement is found for both the reactive (real part) of the response and for the $α$-relaxation peak in the imaginary part, with a significant improvement over earlier theoretical approaches, especially in the reactive modulus. On the low-frequency side of the $α$-peak, the fitting supports the presence of $\sim ω_{p}^{4}$ modes at vanishing eigenfrequency as recently shown in [Phys. Rev. Lett. 117, 035501 (2016)]. $α$-wing asymmetry and stretched-exponential behaviour are recovered by our framework, which shows that these features are, to a large extent, caused by the soft boson-peak modes in the DOS.

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