Baggioli Matteo, Zaccone Alessio
Instituto de Fisica Teorica UAM/CSIC, c/Nicolas Cabrera 13-15, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Crete Center for Theoretical Physics, Institute for Theoretical and Computational Physics, Department of Physics, University of Crete, 71003 Heraklion, Greece.
Phys Rev Lett. 2019 Apr 12;122(14):145501. doi: 10.1103/PhysRevLett.122.145501.
The vibrational spectra of solids, both ordered and amorphous, in the low-energy regime, control the thermal and transport properties of materials, from heat capacity to heat conduction, electron-phonon couplings, conventional superconductivity, etc. The old Debye model of vibrational spectra at low energy gives the vibrational density of states (VDOS) as proportional to the frequency squared, but in many materials the spectrum departs from this law which results in a peak upon normalizing the VDOS by frequency squared, which is known as the "boson peak." A description of the VDOS of solids (both crystals and glasses) is presented starting from first principles. Without using any assumptions whatsoever of disorder in the material, it is shown that the boson peak in the VDOS of both ordered crystals and glasses arises naturally from the competition between elastic mode propagation and diffusive damping. The theory explains the recent experimental observations of boson peak in perfectly ordered crystals, which cannot be explained based on previous theoretical frameworks. The theory also explains, for the first time, how the vibrational spectrum changes with the atomic density of the solid, and explains recent experimental observations of this effect.
在低能区，有序和非晶态固体的振动光谱控制着材料的热学和输运性质，从热容量到热传导、电子 - 声子耦合、传统超导性等。旧的低能振动光谱德拜模型给出的振动态密度（VDOS）与频率平方成正比，但在许多材料中，光谱偏离了这一规律，这导致在将VDOS除以频率平方进行归一化时出现一个峰值，这就是所谓的“玻色子峰”。本文从第一性原理出发，对固体（包括晶体和玻璃）的VDOS进行了描述。在不使用任何关于材料无序性假设的情况下，证明了有序晶体和玻璃的VDOS中的玻色子峰自然地源于弹性模式传播和扩散阻尼之间的竞争。该理论解释了最近在完全有序晶体中玻色子峰的实验观测结果，而基于先前的理论框架无法对此进行解释。该理论还首次解释了振动光谱如何随固体的原子密度变化，并解释了最近关于这种效应的实验观测结果。
