| 研究実績の概要 |
Heat in phononic crystals (PnCs) is carried by phonons, which can behave coherently (wave-like) or incoherently (particle-like) depending on the modes, temperature, and length scales. In the last year, we shown that coherent phonon relaxation time is significantly reduced by Ahkhizer damping at high temperatures, as a result, contribution of coherent phonons to thermal conductivity of PnCs becomes intrinsically small, which indicates that manipulate heat conduction with coherent effect at high temperature is extremely challenging. To investigate the wave nature of phonons at low temperatures, we conducted neutron scattering experiment at J-PRAC at 4 K (No. 2017B0118 and 2018B0209) to measure the dispersion of phonons. The measured results suggest that coherent phonons may exist blow 1 THz.
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| 今後の研究の推進方策 |
For the topic of phonon coherence,we ,last year,have theoretically evaluated the relaxation time of wave phonons, and neutron scattering experiment was performed at J-PARC to direct observe coherence effect at 5 K. In this year, we will continue to push forward the investigation of the wave nature of phonons by molecular dynamics.We will focus on the effect of temperature, roughness and amorphous surfaces on coherent loss from atemperature range of 5 K to 300 K. Additional neutron scattering experiment will be applied at J-PARC.
For the topics of roughness, we will focus on the local properties of PnCs: local distribution of elastic modulus and local phonon scattering rates, which also related to the wave nature of phonons. Molecular and lattice dynamics will be used for these studies.
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