LM thesis proposal
Supervisors: Marco Zanatta & Giacomo Baldi
At the macroscopic scale, an amorphous solid can be considered as an isotropic continuum and sound wave propagation is well described by the usual elasticity theory. However, the thermal properties at low temperatures (below 1 K) are heavily affected by the presence of two-level states whose microscopic origin has remained mysterious. Recent simulations evidenced the presence of quasi-localized vibrational modes besides the extended phonon-like excitations. It seems that these modes dominate the low-energy density of vibrational states and could be the precursors of the two-level systems.
We will study these excitations by means of inelastic neutron scattering at the cold chopper spectrometer IN5 (Institut Laue Langevin, Grenoble, France). During the experiment, we plan to investigate the low-energy (below 1 meV) low-temperature (below 10 K) dynamics of vitreous SiO2, the prototype of strong glasses. A successful determination of its vibrational density of states at such low temperatures and energies will allow us to disentangle the contributions coming from two-level systems and the eventual presence of quasi-localized modes.
References
- G. Baldi et al., Vibrational dynamics of non-crystalline solids, chapter (World Scientific, 2022).
The illustration shows the BP in vitreous SiO2; data are from E. Fabiani et. al., J. Chem. Phys. 128, 244507 (2008)
Starting date: 1/02/2023, the experiment will be done in the first part of 2023.
