Terahertz time-domain spectroscopic study on boson peak of Li_0.25Na_0.25K_0.25Cs_0.25PO₃ glass

Disordered materials exhibit universal dynamics in the terahertz (THz) region, that is, the so-called boson peak. The boson peak observed universally in the THz region is clearly characterized by making a plot which is constructed by the vibrational density of states divided by the squared frequency. In the case of infrared spectrum, the boson peak can be characterized by α(ν)/ν², where α(ν) is the absorption coefficient and ν is infrared frequency. In this study, we performed terahertz time-domain spectroscopy (THz-TDS) on an oxide glass with entropic elasticity: mixed alkali metal metaphosphate glass with the chemical composition Li_0.25Na_0.25K_0.25Cs_0.25PO₃, to detect the boson peak. By comparing the obtained THz-TDS spectra of this sample with results of low-frequency Raman scattering and low-temperature specific heat measurement, we estimated an infrared light-vibration coupling coefficient C_IR(ν) in the THz region. According to C_IR(ν) and a theoretical model, we evaluated the uncorrelated charge of this glass.