Decoding thermal transport mechanisms induced by short-range order in amorphous system

Despite the absence of long-range structural order, amorphous solids retain an atomic-scale short-range ordered environment. However, the mechanisms through which short-range order influences vibrational modes and its subsequent effects on thermal conductivity remain elusive. In this work, we employ molecular dynamics and lattice dynamics simulations to investigate how short-range order modulates vibrational properties and thermal transport in amorphous silicon. Our simulations reveal that rapid cooling rates during the melt-quench process result in amorphous silicon structures with diminished short-range order. This reduction primarily intensifies the scattering of propagative vibrational modes for both transverse and longitudinal polarizations, particularly near the Ioffe-Regel crossover. Consequently, enhanced scattering weakens the mode correlation of propagative modes, further suppressing thermal conductivity. Additionally, our spatial coherence analysis demonstrates that reduced short-range order diminishes the wavelike behavior of propagative modes. Our findings provide a fundamental interpretation of the prevailing concept of mode correlation with the spatial coherence of thermal vibrations in amorphous systems, as well as physical insights into the role of short-range order in the wavelike nature of vibrational modes and the engineering of thermal transport in amorphous materials.