One of the most intriguing puzzles of modern solid state physics is: how do topological stable defects (dislocations, kinks on them, domain walls, Bloch lines etc.) arise and move in highly excited crystals?

In order to solve this fundamental problem we carry out direct experimental investigations of spectra of elementary excitations of different systems as well as of the processes of nonlinear soliton-type waves formation and their subsequent evolution which give rise to nucleation of the topological defects.