1. Physics Department “E. R. Caianiello”University of Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
2. Interdepartmental Centre NanoMatesUniversity of Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
3. CNR‐SPIN Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
4. National Laboratory of Solid State MicrostructuresSchool of PhysicsCollaborative Innovation Center of Advanced MicrostructuresNanjing University Nanjing 210093 China
5. Department of Physical and Chemical ScienceUniversity of L'Aquila, and CNR‐SPIN L'Aquila via Vetoio Coppito 67100 L'Aquila Italy