Raman scattering in ZrB12 cage glass

High-precision measurements of the Hall effect and Raman scattering have been performed for single crystals of ZrB12 superconductor in the wide temperature range of 5–300 K. For ZrB12, the boson peak with ωmax ~ 100 cm–1 has been observed for the first time within the low-frequency range of the Raman spectrum I(ω). The sizes of vibrational clusters with the correlation length ranging from 25 to 35 A are estimated. The relation between the renormalization of the low-frequency density of vibrational states accompanying the transition to the cage-glass phase (T* ~ 90 K) and the enhancement of superconductivity in ZrB12 is discussed.