1. Dipartimento di
Fisica, Università di Roma Tor Vergata, and European Theoretical Spectroscopy Facility (ETSF), Via della Ricerca Scientifica 1, 00133 Roma, Italy
2. Department of Physics, University of California, Berkeley, California 94720, United States
3. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States