1. Department of Physics and Interdepartmental Centre NanoMates, University of Salerno, via Giovanni Paolo II, Fisciano, Salerno 84084, Italy
2. CNR-SPIN, via Giovanni Paolo II, Fisciano, Salerno 84084, Italy
3. IHP-Microelectronics, Im Technologie Park 25, Frankfurt Oder 15236, Germany
4. Department of Physics, Faculty of Science, University of Guilan, 41335-1914 Rasht, Iran