1. Department of Physics, IFM, Linköping University, 58183 Linköping, Sweden, Department of Physics, Humboldt University Berlin, Invalidenstrasse 110, 10115 Berlin, Germany, Université de Mons-Hainaut, Place du Parc 20, 7000 Mons, Belgium, and Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany