Chaotic discrete breathers in bcc lattice

Abstract

It is well known that a modulationally unstable short-wavelength delocalized nonlinear vibrational mode (DNVM) can create chaotic discrete breathers (DBs) in a nonlinear lattice. A necessary condition for this is that the DNVM must have a frequency outside the phonon spectrum of the lattice. This phenomenon has been repeatedly analyzed for one- and two-dimensional lattices, and here it is studied for a bcc lattice with β-Fermi–Pasta–Ulam–Tsingou potential. Using the group-theoretical approach developed by Chechin and Sakhnenko, four DNVMs are found with a wave vector at the boundary of the first Brillouin zone and frequencies above the phonon spectrum. It is shown that the development of the modulational instability of all four DNVMs with amplitudes above a certain value leads to the formation of chaotic DBs, which is justified by calculating the energy localization parameter and the maximum particle energy. Chaotic DBs in the three-dimensional bcc lattice radiate their energy faster than in previously studied two-dimensional lattices. The results obtained describe one of the possible mechanisms of energy dissipation by a crystal lattice in a far-from-equilibrium system.