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. Institute for Applied Physics and Center LISA+, University of Tuebingen, Auf der Morgenstelle 10, 72076, Tuebingen, Germany
4. The Applied Physics Department, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel