1. Physics Department E20Technical University of Munich 85748 Garching Germany
2. Department of Physics, Chemistry and Biology, IFMLinköping University 58183 Linköping Sweden
3. Institute of NanotechnologyKarlsruhe Institute of Technology (KIT) Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany
4. Institute of PhysicsChinese Academy of Sciences 100190 Beijing P. R. China
5. Institute de Physique et Chimie de Matériaux (IPCMS)Université Strasbourg 23 rue du Loess, BP 43 67034 Strasbourg cedex 2 France