1. Department of Physics, University of Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany
2. Lehrstuhl für Funktionelle Materialien, Physik Department E13, Technische Universität München, James-Franck-Str. 1, 85747 Garching, Germany
3. Experimental Systems Advanced Light Source, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, California 94720, United States
4. Department of Physics, National University of Singapore, Lower Kent Ridge Road, Singapore S117542, Singapore