1. Physics Department “E. R. Caianiello” and Interdepartmental centre NanoMates University of Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
2. CNR‐SPIN Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
3. Department of Physical and Chemical Sciences University of L’Aquila and CNR‐SPIN L’Aquila via Vetoio Coppito 67100 Italy
4. Faculty of Sciences HIT‐Holon Institute of Technology Holon 5810201 Israel
5. INFN—Gruppo collegato di Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy