1. Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano, Italy
2. European XFEL, Holzkoppel 4, Schenefeld, D-22869, Germany
3. ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS 40220, F-38043 Grenoble, France
4. Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden
5. CNR-SPIN, Dipartimento di Fisica, Politecnico di Milano, I-20133 Milano, Italy