Research objectives and content
The slow relaxation phenomena observed in glasses are usually interpreted by the existence of many metastable states. George Tsironis and I have recently shown that nonlinear systems without metastable states, may also exhibit similar behaviours. We have also shown that this unexpected feature is essentially a consequence of the property that these systems can sustain long life time breathers (Nonlinear Localized Excitations) which play a role similar to those of metastable states. On the base of the new developments of the theory of breathers to which I participated actively, I propose to collaborate with the group of George Tsironis in Heraklion for performing a detailed analysis of the phenomena in 1 and 2 dimensional models. We shall analyse its consequences on the thermal transport and the dynamical response function of these systems. We shall also study the possibility of defining extended diffusion equations (similar to those used for porous media) which could describe these phenomena. The connection with the famous FPU (Fermi-Pasta-Ulam) numerical experiments showing a poor thermalisation in some anharmonic systems, shall be also investigated. We shall also study the possibility of realizing real experiments exhibiting such slow thermal relaxation for example by probing as a function of time, the relaxation of a thermal grid in appropriate anharmonic materials created by the interference of two short laser pulses.
Training content (objective, benefit and expected impact)
I have been recently involved in the recent breakthrough on the theory of breathers (existence proof in large classes of anharmonic models and other rigorous results). I collaborated recently with George Tsironis for the initial stage of this program. The purpose of the collaboration is to involve PHD students and post-doctoral physicists of Heraklion in this research program.