1. Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, Edifici ICN2, 08193 Bellaterra, Spain
2. NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, I-56127, Italy
3. IEMN, Universite de Lille 1, Villeneuve d’Ascq, France
4. PRILM, Université Moulay Ismail, Faculté des sciences, Meknès, Morocco
5. Depto. Física, Universidad de la Laguna, 38206, Spain
6. Dipartimento di Fisica, Universita di Pisa, Largo Pontecorvo 3, I-56127 Pisa, Italy
7. Nanophotonics Technology Center, Universitat Politècnica de València, Valencia, Spain
8. Catalan Institution for Research and Advanced Studies (ICREA), 08010 Barcelona, Spain