1. Center for Integrated Nanotechnologies, Material Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
2. Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080, United States
3. Ioffe Institute, 194021 St. Petersburg, Russia
4. Department of Physics, Jackson State University, Jackson, Mississippi 39217, United States