1. Department of Physical and Chemical Sciences, University of L’Aquila, via Vetoio, 67100 L’Aquila, AQ, Italy
2. Elettra-Sincrotrone S.C.p.A., S.S. 14-km 163.5 in AREA Science Park, 34149 Trieste, Italy
3. Department of Industrial and Information Engineering and Economics, University of L’Aquila, Via G. Gronchi 18, I-67100 L’Aquila, Italy
4. Department of Physics, National Cheng Kung University, 1 Ta-Hsueh Road, 70101 Tainan, Taiwan
5. Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain
6. Consiglio Nazionale delle Ricerche (CNR)-Istituto Officina dei Materiali (IOM), Laboratorio TASC in Area Science Park S.S. 14 km 163.5, 34149 Trieste, Italy
7. Instituto ‘Nicolás Cabrera’, Universidad Autónoma de Madrid, 28049 Madrid, Spain
8. Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain
9. College of Science, Institute of Materials Physics and Chemistry, Nanjing Forestry University, Nanjing 210037, P. R. China
10. Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
11. CNR-IMM Istituto per la Microelettronica e Microsistemi, VIII strada 5, I-95121 Catania, Italy