Chemical & Biological Physics Department, Weizmann Institute of Science, Rehovot 7610001, Israel.
Phys Rev Lett. 2021 Feb 26;126(8):088004. doi: 10.1103/PhysRevLett.126.088004.
Glasses, unlike their crystalline counterparts, exhibit low-frequency nonphononic excitations whose frequencies ω follow a universal D(ω)∼ω^{4} density of states. The process of glass formation generates positional disorder intertwined with mechanical frustration, posing fundamental challenges in understanding the origins of glassy nonphononic excitations. Here we suggest that minimal complexes-mechanically frustrated and positionally disordered local structures-embody the minimal physical ingredients needed to generate glasslike excitations. We investigate the individual effects of mechanical frustration and positional disorder on the vibrational spectrum of isolated minimal complexes, and demonstrate that ensembles of marginally stable minimal complexes yield D(ω)∼ω^{4}. Furthermore, glasslike excitations emerge by embedding a single minimal complex within a perfect lattice. Consequently, minimal complexes offer a conceptual framework to understand glasslike excitations from first principles, as well as a practical computational method for introducing them into solids.
眼镜与晶体不同，它们表现出低频非声子激发，其频率 ω 遵循普遍的 D(ω)∼ω^{4}态密度。玻璃形成过程产生了位置无序与力学失谐交织在一起的情况，这对理解玻璃非声子激发的起源构成了基本挑战。在这里，我们提出最小复合物——力学失谐和位置无序的局部结构——体现了产生玻璃状激发所需的最小物理成分。我们研究了机械失谐和位置无序对孤立最小复合物振动谱的单独影响，并证明了边缘稳定最小复合物的集合产生 D(ω)∼ω^{4}。此外，通过将单个最小复合物嵌入完美晶格中，可以产生玻璃状激发。因此，最小复合物为从第一性原理理解玻璃状激发提供了一个概念框架，也是在固体中引入它们的实用计算方法。
