Abstract
Lattice heat conduction can be modulated via nanostructure interfaces. Although advances have been made by viewing phonons as particles, the controllability should be enhanced by fully utilizing their wave nature. By considering phonons as coherent waves, herein we design an optimized aperiodic superlattice that minimizes the coherent phonon heat conduction by alternatingly coupling coherent phonon transport calculations and machine learning. The thermal conductivity of the fabricated aperiodic superlattice agrees well with the calculations over a temperature range of 77–300 K, indicating that complex aperiodic wave interference of coherent phonons can be controlled. The thermal conductivity of the aperiodic superlattice is significantly smaller than the conventional periodic superlattice due to enhanced phonon localization. The optimized aperiodic structure is formed by connecting weakly correlated local structures that introduce interference over broad phonon frequencies. Controlling coherent phonons by aperiodic interferences opens a new route for phonon engineering.
- Received 20 June 2019
- Revised 20 March 2020
- Accepted 14 April 2020
DOI:https://doi.org/10.1103/PhysRevX.10.021050
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
By designing the structure of crystalline materials at the nanoscale, researchers have been able to enhance heat conduction by controlling the transport of phonons, the fundamental quanta of mechanical vibrations. A representative case is the superlattice, made by stacking alternating materials with a thickness of several nanometers. So far, advances have been made mostly by modeling phonons as particles, in which scattering at interfaces inhibits heat conduction. However, phonons—like photons—can also be thought of as waves. While utilizing the wavelike effects of phonons is found to be challenging, doing so could lead to significant gains in the ability to control heat conduction. To that end, we design an optimal superlattice structure that fully minimizes heat conduction by taking advantage of the phonon wave nature.
We first design our aperiodic superlattice by coupling coherent phonon transport calculations and machine learning. We then fabricate the structure. Our measurements reveal that the predicted thermal conductivity is realized over a wide range of temperature, solidly demonstrating the successful control of complex aperiodic interference of coherent phonon waves. The thermal conductivity of the aperiodic superlattice is significantly smaller than that of a conventional periodic superlattice. We attribute this improvement to the phonon localization induced by some key local structures, enabling interference of phonons with broad frequencies.
Such controllability and understanding of the aperiodic interference of coherent phonons open a new route for phonon engineering.