1. Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany, Physics Department and Center of Excellence for Nanostructured Materials, University of Trieste, Via Valerio 2, I-34127 Trieste, Italy, Laboratorio TASC INFM-CNR, Area Science Park, I-34012 Trieste, Italy, Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, I-34012 Trieste, Italy, Institute de Physiques des Nanostructures, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland, and Department of...