【講演概要】 

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. By comparing the measured thermal conductivity of PnCs with theories,
recent works suggest that thermal conductivity of PnCs can be explained by
considering only surface and boundary scatterings, which not only backscatter phonons
but also break their coherence. The logic here is that since average phonon wavelength
at room temperature is only a few nanometers, the roughness at the surfaces and
boundaries make the scattering diffusive (break the phase coherence of phonons), and
thus only very long wavelength (low frequency) phonons with negligible contribution
to total thermal conductivity remain coherent. Here, we theoretically show that in a thin
film PnCs, the low frequency coherent phonons could significantly contribute to
thermal conductivity when assuming the three-phonon scattering model for intrinsic
scattering because of their extremely large density of states that result from the low
dimensional nature. Yet, further analysis shows the contribution of the low frequency
coherent phonons is still negligible within temperature range from 130 to 300 K due to
the Akhiezer mechanism, which properly answers the question why the thermal
conductivity of PnCs can be explained by considering only scattering of incoherent
phonons at these temperatures.
 

【キーワード】

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【使用製品】

COMSOL Multiphysics, 音響モジュール
 

【共同著作者】

東京⼤学 機械⼯学専攻 ⼤⻄ 正⼈ 先生
東京⼤学 機械⼯学専攻 塩⾒ 淳⼀郎 先生
 

【English title】

Akhiezer mechanism limits coherent heat conduction in phononic crystals
 

【Keyword】

Phononic crystal, Phonon coherence, Thermal conductivity, Akhiezer damping
 

【講師紹介】

東京大学 機械工学専攻 特任研究員 Liao Yuxuan 先生