Boson Peak and Fracton of Polymethyl Methacrylate Detected by Terahertz-band Infrared and Raman Spectroscopies

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on polymethyl methacrylate to investigate the boson peak (BP) which is a universal excitation in glass, and the fracton which is expected to be expressed in polymer glass. In the infrared spectrum, the BP was observed in the plot of α(ν)/ν
²
, where α(ν) is the absorption coefficient. In addition, the infrared light-vibration coupling constant C
IR
(ν) and the Raman coupling constant C
Raman
(ν) were determined, and the fracton was observed as a linear region in the log-log plots of C
IR
(ν) and C
Raman
(ν).