1. Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
2. Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
3. NEST, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
4. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
5. NEST, Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127 Pisa, Italy
6. National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan