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-field solutions. Here, we report first-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-field 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 identifies 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.

准粒子的概念构成了我们对与量子力学多体相互作用相关的新兴现象的微观理解的理论基础。然而，无序材料中的准粒子理论已被证明是困难的，从而导致平均场解的出现。在这里，我们报告了具有恒定力显性紊乱的等原子合金（NiCo，NiFe，AgPd和NiFeCo）的第一性原理声子计算以及非弹性X射线和中子散射测量结果-面对一个关键的已有50年历史的假设非对角线紊乱的所有均场准粒子解的哈密顿量。我们的结果表明，存在大量的，迄今无法识别的，局部化学环境对能控制声子散射的物种对分辨力常数分布的影响。这一发现不仅确定了对其他基本激发（例如磁性合金中的磁振子和天体离子）具有广泛影响的关键分析问题，而且为设计具有超低导热率的材料提供了重要工具。