1. Istituto di Struttura
della Materia (ISM), Consiglio Nazionale delle Ricerche (CNR), I-34149 Trieste, Italy
2. S3-Istituto di Nanoscienze-CNR, Via
Campi 213/A, I-41125 Modena, Italy
3. Institute of Condensed
Matter Physics (ICMP), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station
3, CH-1015 Lausanne, Switzerland
4. Institute
of Theoretical Physics and Astrophysics, University of Kiel, D-24098 Kiel, Germany
5. Department
of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
6. Dipartimento
di Fisica, Università della Calabria, I-87036 Arcavacata
di Rende (Cs), Italy
7. Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland