Bridging the Attenuation Gap of Longitudinal Acoustic Phonons in Vitreous Silica with Terahertz Photoacoustic Spectroscopy

Peng-Jui Wang^1*, Jin-Kong Sheu², Chi-Kuang Sun¹

¹Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan
²Department of Photonics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan

* Presenter:Peng-Jui Wang, email:f03941016@ntu.edu.tw

Understanding the phonon transport in disordered materials can help us elucidate a long-standing debate in regard to the excess vibrational modes anomalies in amorphous materials at low temperatures, also known as boson peak. It has been intensively studied over the past four decades, but the most critical evidence is missing because of a lack of measurement techniques in the THz to sub-THz range. Here we demonstrate that the sound transport behavior in vitreous silica (v-SiO2) is measured via the advanced THz photoacoustic transceiver with a bandwidth over 2 THz which could bridge the aforesaid spectral gap. This research provides not only the sound attenuation spectra but also the phonon dispersion in v-SiO2, and our analysis show a quartic frequency dependence damping relation. Our attenuation-momentum relation further points out the dominant mechanism in the boson peak anomaly from the soft potential model (SPM) and Rayleigh scattering mechanism, which have been considered as the main mechanisms.

Keywords: boson peak, phonon, terahertz acoustic spectroscopy, vitreous silica, amorphous