1. CNR-IOM, Unità SLACS, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato (CA), Italy
2. Department of Physics, University of Cagliari, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato (CA), Italy
3. School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
4. Cluster of Excellence Frankfurt - Macromolecular Complexes and Institute of Biochemistry, Goethe University Frankfurt, Max-von-Laue-Str.9, D-60438 Frankfurt am Main, Germany
5. Physik-Department, Technische Universität München, James-Franck-Str. 1, D-85748 Garching, Germany