Driven Intrinsic Localized Modes in Soft Nonlinear Microscopic and Macroscopic Lattices

The possibility that large amplitude, localized vibrational excitations can exist in periodic physical lattices with nonlinear intersite forces was discovered over thirty years ago. The energy profiles of these intrinsic localized modes (ILMs) resemble those of localized vibrational modes at defects in a harmonic lattice. Described here are a variety of experiments on driver locked ILMs for two soft nonlinear lattices: an atomic spin array and an electrical nonlinear transmission line. CW locked ILMs in the quasi-1D antiferromagnet (C2H5NH3)2CuCl4 have been found at frequencies below the antiferromagnetic resonance by employing four-wave mixing emission. A discrete step structure is observed in the emission signal as well as repeatable nonlinear ILM switching and hysteresis. These findings are compared with locked ILMs and large amplitude lattice spatial modes (LSMs) that have been measured for a driven 1-D nonlinear cyclic electric transmission line, where the nonlinear element is a saturable capacitor. Interestingly, by tuning the driver frequency away from the modal spectrum an LSM can be continuously converted into ILMs and vice versa. As a consequence, the resultant electrical energy distribution for the experimental soft nonlinear cyclic array can be either balanced or unbalanced.