Phonon interpretation of the 'boson peak' in supercooled liquids
Phonon interpretation of the 'boson peak' in supercooled liquids
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DOI：
10.1038/nature01475
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发表时间：
2003-03-20
期刊：
影响因子：
64.8
通讯作者：
Verrocchio, P
中科院分区：
文献类型：
--
作者：
Grigera, TS;Martín-Mayor, V;Verrocchio, P
玻璃(1，2)是无定形固体，因为它们表现出弹性行为。在晶体固体中，弹性与声子有关，声子是量子化的振动激发。在非常高的(太赫兹；10(12)赫兹)频率下，玻璃中也存在类声子激发；令人惊讶的是，这些激发在过冷液体中持续存在。这种非晶态系统的一个普遍特征是玻色子峰值：与德拜平方频率定律相比，态的振动密度有一个过剩。在这里，我们通过研究真实玻璃模型中固有结构的光谱(势能的局部极小值)来研究这一特征的起源。我们认为，该峰值是能量驻点空间中从低能极小主相(有声子)到鞍点主相(5-7)(无声子)相变的标志。在接近声子-鞍形转变时，玻色子峰向低频移动，其高度在临界点发散。我们的数值结果与欧几里德随机矩阵理论(8)关于在非晶弹性相和无声子相之间存在尖锐相变(9)的预测一致。
Glasses(1,2) are amorphous solids, in the sense that they display elastic behaviour. In crystalline solids, elasticity is associated with phonons, which are quantized vibrational excitations. Phonon-like excitations also exist in glasses at very high (terahertz; 10(12) Hz) frequencies; surprisingly, these persist in the supercooled liquids'. A universal feature of such amorphous systems is the boson peak: the vibrational density of states has an excess compared to the Debye squared-frequency law. Here we investigate the origin of this feature by studying the spectra of inherent structures' (local minima of the potential energy) in a realistic glass model. We claim that the peak is the signature of a phase transition in the space of the stationary points of the energy, from a minima-dominated phase (with phonons) at low energy to a saddle-point-dominated phase(5-7) (without phonons). The boson peak moves to lower frequencies on approaching the phonon-saddle transition, and its height diverges at the critical point. Our numerical results agree with the predictions of euclidean random matrix theory(8) on the existence of a sharp phase transition(9) between an amorphous elastic phase and a phonon-free one.