Revisiting the mechanisms of thermal transport in vacancy-defective silicon

Conventional understanding on thermal conduction mechanisms in defective crystals is based on the phonon gas picture, treating defects as scattering centers that reduce phonon lifetimes without altering frequencies and group velocities. However, this theory overlooks fundamental consequences of defects: they break crystal symmetry and disrupt the definition of unit cells, which may fundamentally alter the nature of heat transport. The authors go beyond the phonon gas picture here, and establish a computational framework combining the Wigner transport equation with normal-mode decomposition. They reveal that the emergence of wavelike effects and defect-induced modifications to velocity operators in vacancy-defective silicon are critical previously underappreciated mechanisms.