1. Department of Physics; The George Washington University; 725 21st Street, NW Washington DC 20052 USA
2. On leave of absence: Institute of Radiophysics and Electronics; National Academy of Sciences; 1 Brothers Alikhanyan st. Ashtarak 0203 Armenia
3. Centre Interdisciplinaire de Nanoscience de Marseille, CINaM; UMR 7325 CNRS - Aix-Marseille Université; Campus de Luminy, Case 913, 163 Avenue de Luminy 13288 Marseille cedex 9 France