1. Department of Physics, City College of New York, New York, NY 10031, USA.
2. Department of Physics, University of Regensburg, 93040 Regensburg, Germany.
3. Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany.
4. Department of Physics, The Graduate Center, City University of New York, New York, NY 10016, USA.
5. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki 305-004, Japan.
6. Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-004, Japan.
7. Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Würzburg-Dresden Cluster of Excellence ct.qmat, Dresden University of Technology, Dresden 01187, Germany.