50多年来，由于与布洛赫定理中描述的完全有序晶体不同，无序合金中平移对称性的破坏，长期以来一直挑战着类似的准粒子理论的发展，因此，描述无序材料中准粒子的光谱色散和寿命，对于理解凝聚态的基础科学和具有目标性质的材料设计具有重要意义。
来自美国橡树林国家实验室的.George M. Stocks教授，通过第一原理计算，结合对浓缩的、带有很强力常数紊乱却几无质量紊乱的无序合金NiCo、NiFe、AgPd和NiFeCo所作的声子准粒子物理学（色散和线宽）实验测量，发现存在一个巨大的、迄今未被认识的、局部化学环境对物种对-分辨的力学常数无序分布的影响，而这恰恰是影响声子散射的主要因素。值得注意的是，在从头算的超胞声子展开（SPU）模拟，及其与ICPA和实验测量的比较中，考虑到每个单独的AA、BB和AB型物种对,力常数的变化远远超过了通常的全局平均力常数波动。此外，他们的研究结果表明，增强型磁阻的来源，是围绕着单个AA、BB和AB型物种对的局部化学环境所固有的随机变化。因此，以往长期使用的近似方法（用无序材料的准粒子平均-Er场理论的哈密顿量的全局平均值，来代替单个物种对的力常数波动），现在必须重新考虑。这一发现不仅找到了问题的要害，而且对研究其他元素的激发态，如磁合金中的磁子和斯格明子的研究将产生广泛影响，而且为超低热导率材料的设计也提供了重要工具。
该文近期发表于npj Computational Materials 6: 4 (2020)，英文标题与摘要如下，点击https://www.nature.com/articles/s41524-020-0271-3可以自由获取论文PDF。
Unfolding the complexity of phonon quasi-particle physicsin disordered materials
Sai Mu, Raina J. Olsen, Biswanath Dutta, Lucas Lindsay, German D. Samolyuk, Tom Berlijn, Eliot D. Specht, KeJin, Hongbin Bei, Tilmann Hickel , Bennet C. Larson and George M. Stocks
The concept of quasi-particles forms the theoretical basis of our microscopic understanding of emergent phenomena associated with quantum-mechanical many-body interactions. However, the quasi-particle theory in disordered materials has proven difficult, resulting in the predominance of mean-eld solutions. Here, we report rst-principles phonon calculations and inelastic X-ray and neutron-scattering measurements on equiatomic alloys (NiCo, NiFe, AgPd, and NiFeCo) with force-constant dominant disorder— confronting a key 50-year-old assumption in the Hamiltonian of all mean-eld quasi-particle solutions for off-diagonal disorder. Our results have revealed the presence of a large, and heretofore unrecognized, impact of local chemical environments on the distribution of the species-pair-resolved force-constant disorder that can dominate phonon scattering. This discovery not only identies a critical analysis issue that has broad implications for other elementary excitations, such as magnons and skyrmions in magnetic alloys, but also provides an important tool for the design of materials with ultralow thermal conductivities.
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