近日，挪威卑尔根大学的Bodil Holst及其研究小组取得一项新进展。经过不懈努力，他们观测到二维材料中的玻色子峰。相关研究成果已于2023年9月4日在国际知名学术期刊《自然—物理学》上发表。
通过采用非弹性氦原子散射测量声子光谱，本文提供了二维二氧化硅中玻色子峰存在的实验证据。研究人员将玻色子峰确定为与波数无关的光谱最大值，其频率与在块状玻璃二氧化硅中观察到的和预测的频率相似。此外，研究人员提出了一种二维的非均质弹性理论计算，该计算显示了横向和弯曲剪切垂直声子模式的振动耦合如何在二维材料中以与块状材料中相似的频率产生玻色子峰。这一理论与他们的测量结果一致。
据悉，玻色子峰是相对于德拜模型的状态声子振动密度中的过剩。这种现象在从无机玻璃到聚合物的各种非晶态材料中都被观察到过。二维随机矩阵模型和分子动力学模拟预测，玻色子峰也应该存在于非晶二维材料中。这一概念具有实际意义，因为它会导致热容量过剩并影响输运性质。 然而，到目前为止，由于通常用于测量玻色子峰的方法的表面灵敏度有限，无法在实际材料中进行实验观测。
附：英文原文
Title: Observation of the boson peak in a two-dimensional material
Author: Tmterud, Martin, Eder, Sabrina D., Bchner, Christin, Wondraczek, Lothar, Simonsen, Ingve, Schirmacher, Walter, Manson, Joseph R., Holst, Bodil
Issue&Volume: 2023-09-04
Abstract: The boson peak is an excess in the phonon vibrational density of states relative to the Debye model. It has been observed in a wide range of amorphous materials, from inorganic glasses to polymers. Two-dimensional random matrix models and molecular dynamics simulations predict that the boson peak should also be present in amorphous two-dimensional materials, a notion that is of practical importance because it leads to an excess of heat capacity and influences transport properties. However, up until now, experimental observations in actual materials have not been possible due to the limited surface sensitivity of the methods usually applied to measure the boson peak. Here we present the experimental evidence of a boson peak in two-dimensional silica, through phonon spectra measured by means of inelastic helium-atom scattering. We identify the boson peak as a wavenumber-independent spectral maximum at a frequency similar to what has been observed in and predicted for bulk vitreous silica. Furthermore, we present a heterogeneous-elastic theory calculation in two dimensions, which shows how the vibrational coupling of the transversal and flexural shear vertical phonon modes produces the boson peak in two-dimensional materials at a frequency similar to that of the bulk, in agreement with our measurements.
DOI: 10.1038/s41567-023-02177-2
Source: https://www.nature.com/articles/s41567-023-02177-2