1. Institute of Physics (PHI)Karlsruhe Institute of Technology (KIT) Wolfgang‐Gaede‐Str. 1 D‐76131 Karlsruhe Germany
2. Institute of Nanotechnology (INT) and Institute of Quantum Materials and Technology (IQMT)Karlsruhe Institute of Technology (KIT) Hermann‐von‐Helmholtz‐Platz 1 D‐76344 Eggenstein‐Leopoldshafen Germany
3. Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS)CNRSUniversité de Strasbourg 23 rue du Loess, BP 43 F‐67034 Strasbourg Cedex 2 France