1. Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
2. The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
3. Materials Physics & Applications Division: Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
4. Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA
5. The Applied Physics Department, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel