Coherent Phonon Heat Conduction in Superlattices

Abstract

Coherent Heat Flow Typically, heat in solids is transported incoherently because phonons scatter at interfaces and defects. Luckyanova et al. (p. 936 ) grew super-lattice films made from one to nine repeats of layers of GaAs and AlAs, each 12-nm thick. Thermal conductivity through this sandwich structure increased linearly with the number of superlattice repeats, which is consistent with theoretical simulations of coherent heat transport.

Diffraction of Quantum Dots Reveals Nanoscale Ultrafast Energy Localization

“…3 and 19; and ii) as adopted in Ref. 20, by performing a spectral average of the frequency-dependent mean-free path 21 extended over the range of the acoustic phonons created by the decay of the LO phonon 18 .…”

Thermal transport in phononic crystals and the observation of coherent phonon scattering at room temperature

“…Thus, the existence of coherent scattering would enable further reduction of the thermal conductivity of the underlying material without the need for additional boundaries (for example, more air holes) by simply optimizing the PnC geometry. While coherent phonon boundary scattering has been observed at low temperatures (30-150 K) in 1D superlattices 11 , it has yet to be observed and verified in two-dimensional (2D) or threedimensional (3D) PnCs, let alone at room temperature.…”

Green's function studies of phonon transport across Si/Ge superlattices

“…The thermal conductivity of superlattices can be even lower than their alloy counterparts [5][6][7][8]. Although diffuse scattering at interfaces is responsible for the remarkable thermal conductivity reduction [9,10], coherent phonon transport has been experimentally observed in GaAs/AlAs superlattices [11] and perovskite oxides [12]. To further reduce the thermal conductivity for thermoelectric applications, it is crucial to understand and control the different phonon transport modes in superlattices.…”

“…Lattice dynamics based on damped wave functions was used to predict a minimum in the thermal conductivity * Corresponding author: gchen2@mit.edu of superlattices in the cross-plane direction [17,18]. More recently, a perturbation method based on the Fermi golden rule [11,19,20] was developed, but the method may have limitations on treating interface scattering, as strong scattering may not be captured by perturbation. One alternative approach is to use molecular dynamics simulations [21,22], which do not assume the nature of phonon transport but are classical in nature.…”

“…We calculate the phonon transmission and corresponding thermal conductivity of Si/Ge superlattices with varying interface roughnesses. Inspired by recent experiments [11], we keep the period thickness of the superlattices fixed while changing the number of periods. We observe coherent phonon transport in smooth-interfaced superlattices, and partially coherent and partially incoherent transport in rough-interfaced superlattices.…”