1. Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
2. Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, St. Gallen CH-9014, Switzerland
3. Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy
4. Department of Physics and Materials Science, University of Luxembourg, 162a, avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg
5. Department of Electrical and Computer Engineering, Rice University, 6100 Main Street MS-378, Houston, Texas 77005, United States
6. Faculty of Science and Technology Free University of Bozen, Piazza Università 5, 39100 Bolzano, Italy