1. National Enterprise for Nanoscience and Nanotechnology (NEST), Consiglio Nazionale delle Ricerche (CNR)−Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, I-56127 Pisa, Italy
2. Laboratoire Charles Coulomb UMR 5221, Centre National de la Recherche Scientifique (CNRS)−Université Montpellier, Place Eugène Bataillon CC074, F-34095 Montpellier, France
3. Graphene Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, I-16163 Genova, Italy
4. Dipartimento di Fisica dell’Universit di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy
5. CENTERA Laboratories, Institute of High Pressure Physics, Polish Academy of Sciences, 01-142 Warsaw, Poland