1. Helmholtz Institute Erlangen-Nürnberg for Renewable Energy, Forschungszentrum Jülich 1 , Cauerstr. 1, D-91058 Erlangen, Germany
2. Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg 2 , Cauerstr. 1, D-91058 Erlangen, Germany
3. Department of Chemical and Biological Engineering and Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg 3 , Cauerstr. 1, D-91058 Erlangen, Germany