Two-dimensional discrete breathers: Construction, stability, and bifurcations

We develop a methodology for the construction of two-dimensional discrete breather excitations. Application to the discrete nonlinear Schrodinger equation on a square lattice reveals three different types of breathers. Considering an elementary plaquette, the most unstable mode is centered on the plaquette, the most stable mode is centered on its vertices, while the intermediate (but also unstable) mode is centered at the middle of one of the edges. Below the turning points of each branch in a frequency-power phase diagram, the construction methodology fails and a continuation method is used to obtain the unstable branches of the solutions until a triple point is reached. At this triple point, the branches meet and subsequently bifurcate into the final, state of an extended phonon mode.