Phonon-Defect Scattering: Success and Breakdown of the T-matrix Approximation

Understanding and predicting phonon transport in disordered compounds is critical to the design and developpment of new functional materials for thermal and energy applications. The T-matrix method, based on the single-scatterer approximation, has been used extensively to incorporate the influence of defects on phonon lifetimes and transport from first-principles. However, the validity of this approximation has not been investigated despite its use in strongly disordered materials such as maximally disordered alloys, for which multiple-impurity scatterings might be expected to play a role. Using the Chebyshev polynomials Green’s function method to unfold the phonon spectrum of large disordered supercells (tens of millions of atoms), we evaluate the phonon-defect scattering rate in mass-disordered alloys and two-dimensional systems featuring atomic vacancies.¹ We explain the surprising success of the T-matrix approximation in predicting the thermal conductivity of even mass-disordered alloys, and find out-of-plane vibrations in monolayers to be especially sensitive to multiple-impurity scattering effects.

1. S. Thébaud, C. A. Polanco, L. Lindsay, and T. Berlijn, Phys. Rev. B 102, 094206 (2019), Success and Breakdown of the T-Matrix Approximation for Phonon-Disorder Scattering