Quantum mechanical analyses of nanoscale phonon transport

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The research achievements under the support of JSPS fellowship mainly include three aspects:(1) We develop the three-dimensional anharmonic phonon non-equilibrium Green’s function formalism, and a parallelized computational framework for large-scale quantum heat transport simulation. With the new methodology, the open question of how anharmonic phonon-phonon scattering plays the role in heat transport at solid-solid interface is studied with a local spectral energy exchange decomposition scheme. Also we present a novel path to demonstrate phonon localization in graded superlattices and a thermal conductivity minimum phenomenon in the quantum coherent regime.(2) We develop a mesoscopic simulation framework based on the phonon Boltzmann equation under Callaway’s dual relaxation model with fully ab initio input of phonon properties for both isotropic and anisotropic material systems. With the new method, we investigate the size effect of phonon hydrodynamics in graphitic nano- and micro-structures, and promote the experimental observation of phonon Poiseuille flow in micro-meter-scale isotopically purified graphite ribbon.(3) We develop a coupled model for heat transport along polar dielectric nanostructures via phonons and surface phonon polaritons. A universal quantum of two-dimensional heat transport in ultrathin polar films is derived for surface phonon polaritons. The non-linear temperature profile due to the coupled dynamics is also demonstrated.