[1] Univ Uniroma TRE, Dept Phys E Amaldi, Rome, Italy
[2] Univ Pavia, Dept Phys A Volta, I-27100 Pavia, Italy
[3] Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA
[4] Iowa State Univ, Ames Lab, Ames, IA 50011 USA
[5] Tech Univ Carolo Wilhelmina Braunschweig, Inst Condensed Matter Phys, D-38106 Braunschweig, Germany
[6] Univ Florence, INSTM, I-50019 Sesto Fiorentino, Italy
[7] Univ Florence, Dept Chem U Schiff, I-50019 Sesto Fiorentino, Italy
[8] Univ Cagliari, INSTM, Cagliari, Italy
[9] Univ Cagliari, Dept Chem Sci, Cagliari, Italy
[10] Univ Milan, Dept Mol Sci Appl Biosyst, I-20134 Milan, Italy
[11] S3 CNR, Inst Neurosci, I-41125 Modena, Italy