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Origin of micron-scale propagation lengths of heat-carrying acoustic excitations in amorphous silicon

Kim, Taeyong and Moon, Jaeyun and Minnich, Austin J. (2020) Origin of micron-scale propagation lengths of heat-carrying acoustic excitations in amorphous silicon. . (Unpublished)

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The heat-carrying acoustic excitations of amorphous silicon are of interest because their mean free paths may approach micron scales at room temperature. Despite extensive investigation, the origin of the weak acoustic damping in the heat-carrying frequencies remains a topic of debate. Here, we report measurements of the frequency-dependent mean free path in amorphous silicon thin films from ∼0.1−3 THz and over temperatures from 60 - 315 K using picosecond acoustics and transient grating spectroscopy. The mean free paths are independent of temperature and exhibit a Rayleigh scattering trend from ∼0.3−3 THz, below which the trend is characteristic of damping from density fluctuations or two-level systems. The observed trend is inconsistent with the predictions of numerical studies based on normal mode analysis but agrees with diverse measurements on other glasses. The micron-scale MFPs in amorphous Si arise from the absence of Akhiezer and two-level system damping in the sub-THz frequencies, leading to heat-carrying acoustic excitations with room-temperature damping comparable to that of other glasses at cryogenic temperatures.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Minnich, Austin J.0000-0002-9671-9540
Additional Information:The authors acknowledge discussions with A. B. Robbins and B. C. Daly. This work was supported by the 2018 GIST-Caltech Research Collaboration.
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GIST-Caltech Research CollaborationUNSPECIFIED
Record Number:CaltechAUTHORS:20200824-140943584
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105081
Deposited By: Tony Diaz
Deposited On:24 Aug 2020 21:18
Last Modified:24 Aug 2020 21:18

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