Impacts of Mingo’s Theories on Thermal Transport Measurements of Materials

This presentation is a reflection of the impacts that Natalio Mingo’s theories have had on thermal transport measurements made by an experimental group. Prior to establishing the widely used ShengBTE open source codes for first-principles theoretical calculation of phonon transport, Mingo advanced a full dispersion transmission function approach and related methods to analyze the size-confinement effects on the lattice thermal conductivity and thermoelectric transport in one-dimensional (1D) semiconductor nanowires that were measured with microfabricated electro-thermal platforms. His subsequent first-principles and atomic Green’s function calculations have clarified the roles of high-order phonon processes and local non equilibrium in microbridge measurements of the length-dependent thermal conductivity and quantized phonon conductance in 1D nanotubes and nanowires. For two-dimensional (2D) materials, his first-principles calculations reveal opposite thickness-dependent behaviors of the lattice thermal conductivity of suspended flat and puckered systems with quadratic and linear flexural vibrational modes, respectively, while his perturbation theoretical model has illustrated the role of substrate-phonon scattering on the measured thermal conductivity in supported 2D graphene. For three-dimensional (3D) simple bulk crystal structures, his Green’s function calculation and T matrix method have allowed for parameter free, atomistic ab initio calculation of defect scattering of phonons in boron arsenide (BAs), enabling the finding of impurity dopants with minimum effects on the unusual high thermal conductivity that has been demonstrated in this compound semiconductor via a phonon band engineering paradigm. In complex 3D crystals, his diffuson-propagon model has explained the measured low lattice thermal conductivity in thermoelectric silicides with a Nowontny chimney ladder structure, whereas low-lying gapped excitations of the lattice and spin dynamics have been observed both in his calculations and inelastic neutron scattering measurements of this and another incommensurate spin ladder compound. The theoretical insights offered by Natalio Mingo have lightened the journeys of many experimentalists in the study of thermal transport of materials over the past two decades.