This individual investigator award supports a research program focused on the experimental investigation of nonlinear nanoscale localization phenomena and discrete pattern formation in condensed matter physics. One way to produce such intrinsic energy localization over a nanoscale region is by making use of the modulational instability of specific large amplitude nonlinear plane wave excitations. To better understand the pathways from plane wave instability to nanoscale energy localization in crystals, three different classes of experiments will be carried out: (a) Intrinsic localized modes (ILMs) in 1D micromechanical arrays will make possible the study of the long time production of monochromatic energy localization phenomena. (b) Intrinsic localized spin wave modes in classical 1D-like antiferromagnetic crystals will be studied in an attempt to observe the newly predicted localized spin flop, which represents a more localized and larger energy excitation than does an ILM. (c) Intrinsic nanoscale energy localization in quantum antiferromagnets and also in soft mode paraelectric crystals will be investigated using high-intensity broadband THz radiation produced at the Jefferson Laboratory. In carrying out nonlinear experiments coupled with numerical simulations both graduate and undergraduate students will develop expertise in this developing interdisciplinary field.
Both nonlinearity and lattice discreteness have played important roles in many branches of physics. The traditional approach in condensed matter physics has been to treat these two items separately. Recently it has been predicted and realized that completely new kinds of dynamical phenomena occur in strongly nonlinear discrete systems. For example, large amplitude long wavelength vibrations in a solid can rapidly cascade down and localize at the atomic scale with a large increase in the vibrational amplitude. The resulting discrete nanoscale patterns in the crystal are predicted to give rise to different physical states. This experimental research program explores such new phenomena. The rapid growth of scientific activity in nonlinear energy localization behavior has shown there are a variety of areas where these effects may play a role, such as friction, and crack propagation. Still other developing areas involve somewhat larger length scales such as optical switches, nonlinear photonic crystal waveguides, periodic electrical Josephson junction arrays, micro-electrical-mechanical silicon systems, and, at the largest scale, the localization within multibunch modes in high energy accelerators. Graduate and undergraduate students working on this project will receive training in nonlinear dynamics in condensed matter systems involving technologically important length scales.
