Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands.
Chemical and Biological Physics Department, Weizmann Institute of Science, Rehovot 7610001, Israel.
Phys Rev Lett. 2018 Aug 3;121(5):055501. doi: 10.1103/PhysRevLett.121.055501.
It is now well established that structural glasses possess disorder- and frustration-induced soft quasilocalized excitations, which play key roles in various glassy phenomena. Recent work has established that in model glass formers in three dimensions, these nonphononic soft excitations may assume the form of quasilocalized, harmonic vibrational modes whose frequency follows a universal density of states D(ω)∼ω^{4}, independently of microscopic details, and for a broad range of glass preparation protocols. Here, we further establish the universality of the nonphononic density of vibrational modes by direct measurements in model structural glasses in two dimensions and four dimensions. We also investigate their degree of localization, which is generally weaker in lower spatial dimensions, giving rise to a pronounced system-size dependence of the nonphononic density of states in two dimensions, but not in higher dimensions. Finally, we identify a fundamental glassy frequency scale ω_{c} above which the universal ω^{4} law breaks down.
现在已经证实，结构玻璃具有由无序和挫折引起的软准局域激发，这些激发在各种玻璃现象中起着关键作用。最近的工作已经证实，在三维模型玻璃形成体中，这些非声子软激发可能采取准局域、谐振动模式的形式，其频率遵循普适的态密度 D(ω)∼ω^{4}，与微观细节无关，并且在广泛的玻璃制备方案范围内。在这里，我们通过在二维和四维模型结构玻璃中的直接测量，进一步确定了振动模式的非声子态密度的普遍性。我们还研究了它们的局域化程度，在较低的空间维度中通常较弱，这导致二维中声子态密度的显著系统尺寸依赖性，但在更高的维度中则没有。最后，我们确定了一个基本的玻璃频率标度 ω_{c}，超过这个标度，普适的 ω^{4}定律就会失效。
