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Coherent Phonon Transport in Complex Oxide Superlattices

Measured values of thermal conductivity for superlattices as a function of superlattice interface density.

Scientific Achievement
Demonstrated coherent phonon transport at a macroscopic scale.

Significance and Impact
Realization and manipulation of wave-nature of phonons has the potential to enable advances in novel heat transfer applications.

Elementary particles such as electrons or photons are frequent subjects of wave-nature-driven investigations. However, collective excitations such as phonons are not given nearly as much attention. The demonstration of wave-particle crossover, in terms of macroscopic properties, is crucial to the understanding and application of the wave behavior of matter. The Thermoelectrics team at Berkeley Lab presents an unambiguous demonstration of the theoretically-predicted crossover from diffuse to specular phonon scattering in oxide superlattices, manifested by a minimum in lattice thermal conductivity as a function of interface density.

This demonstration was achieved by synthesizing superlattices of electrically insulating perovskite oxides and systematically varying the interface density, and measuring thermal conductivity. The existence of a minimum in thermal conductivity as a function of interface density indicates the crossover from particle-like to wave-like transport of phonons, and is one of the important predictions regarding thermal transport across superlattices. These observations open the opportunity for studies on the wave nature of phonons, with extenstive applications in thermoelectrics and thermal management.

J. Ravichandran et al., Nature Materials 13(2), 2014, DOI: 10.1038/NMAT3826