From Transverse Phonons to the Boson Peak: Probing the Vibrational Correlations in Amorphous Materials

In the past, little was known about the momentum dependence or spatial correlation of the transverse phonon and the Boson peak (BP) in amorphous materials. Here, we report the observation of high-frequency transverse phonons [1] and the BP [2] in model Zr-Cu-Al metallic glasses over a wide range of momentum transfer, using inelastic neutron scattering, heat capacity, Raman scattering measurements, and molecular dynamics (MD) simulations. The apparent peak width of the transverse phonons is found to follow the static structure factor, S(Q). The BP energy is largely dispersionless; however, the BP intensity is found to scale with the S(Q) too. Additional MD simulations with a generic Lennard-Jones potential confirm the same. Based on these results, an analytical expression for the dynamic structure factor is formulated for the BP excitation. Further analysis of the simulated disordered structures suggests that the BP is related to local structure fluctuations (e.g., in shear strain). Our results offer insights into the nature of the BP and provide guidance for the development of dynamic theories of amorphous materials.

References

 Xiyang Li^†, H. P. Zhang^†, S. Lan^†, D. L. Abernathy, T. Otomo, F. W. Wang, Y. Ren, M. Z. Li*, and X. L. Wang*, “Observation of High-frequency Transverse Phonons in Metallic Glasses”, Physical Review Letters 124, 225902 (2020).

Xiyang Li^†, H. P. Zhang^†, S. Lan, D. L. Abernathy, C. H. Hu, L. R. Fan, M. Z. Li*, and X. L. Wang*, “Spatial Correlation at the Boson Peak Frequency in Amorphous Materials”, Nature Communications to appear.