Moving Discrete Breathers in 2D and 3D Crystals

Abstract

Discrete breathers (DB), also known as intrinsic localized modes, are spatially localized large-amplitude vibrational modes in defect-free anharmonic lattices. Crystals can be regarded as anharmonic lattices and it is natural to expect that they support DB. The role of DB in the solid state physics is not yet well understood because their experimental detection is difficult. Nevertheless there exist a large number of theoretical works where the existence conditions and properties of DB in crystals have been analyzed. The key issue actively discussed in the literature is the mobility of DB. Moving DB can be a carrier of energy, momentum, electric charge, etc. A DB can localize energy of the order of 1 eV, while collision of propagating DB can result in even higher energy localization. The high energy density regions in crystals can act as the sources of crystal lattice defects, they can initiate fracture or phase transitions. In this chapter the anzats for generating moving discrete breathers in monatomic crystals is offered and successfully tested in molecular dynamics simulations for the 2D Morse crystal and hcp cobalt and magnesium. It is then demonstrated that two colliding DB can produce a DB with greater amplitude. Gap DB wandering in an ionic crystal with NaCl structure are described.