Localizing Energy Through Nonlinearity and Discreteness
Dr. Sergej Flach (Max-Planck-Institut für Physik komplexer Systeme, Dresden)

Intrinsic localized modes, or discrete breathers, localize energy of excitations in spatially extended systems in the absence of disorder. The key ingredients are nonlinearity and spatial discreteness. These modes have been theoretical constructs for more than a decade. Only recently have they been observed in physical systems as distinct as charge-transfer solids, Josephson junction networks, photonic structures, Bose-Einstein condensates on optical lattices, and micromechanical oscillator arrays. The first part of the talk will introduce the theoretical concepts, including a brief discussion of experimental observations and open problems. In the second part I will present a new application to the properties of normal mode interactions in reciprocal space. The outcome - exact periodic orbits which localize energy in normal mode space - solve major parts of the famous Fermi-Pasta-Ulam problem of nonequipartion of mode energies in a nonlinear atomic chain.