Boson peak dynamics of glassy glucose studied by integrated terahertz-band spectroscopy

Abstract

We performed terahertz time-domain spectroscopy, low-frequency Raman scattering, and Brillouin light scattering on vitreous glucose to investigate the boson peak (BP) dynamics. In the spectra of $\ensuremath{\alpha}(\ensuremath{\nu})/{\ensuremath{\nu}}^{2}$ $\mathrm{[}\ensuremath{\alpha}(\ensuremath{\nu})$ is the absorption coefficient], the BP is clearly observed around 1.1 THz. Correspondingly, the complex dielectric constant spectra show a universal resonancelike behavior only below the BP frequency. As an analytical scheme, we propose the relative light-vibration coupling coefficient (RCC), which is obtainable from the combination of the far-infrared and Raman spectra. The RCC reveals that the infrared light-vibration coupling coefficient ${C}_{\mathrm{IR}}(\ensuremath{\nu})$ of the vitreous glucose behaves linearly on frequency which deviates from Taraskin's model of ${C}_{\mathrm{IR}}(\ensuremath{\nu})=A+B{\ensuremath{\nu}}^{2}$ [S. N. Taraskin et al., Phys. Rev. Lett. 97, 055504 (2006)]. The linearity of ${C}_{\mathrm{IR}}(\ensuremath{\nu})$ might require modification of the second term of the model. The measured transverse sound velocity shows an apparent discontinuity with the flattened mode observed in the inelastic neutron scattering study [N. Violini et al., Phys. Rev. B 85, 134204 (2012)] and suggests a coupling between the transverse acoustic and flattened modes.