1. Materials Science and Technology Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
2. Materials Science and Technology Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA, and Department of Physics and Center for Nonlinear Science, University of California, Santa Barbara, CA 93106, USA.
3. Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
4. Department of Physics and Center for Nonlinear Science, University of California, Santa Barbara, CA 93106, USA.