1. Physikalisches
Institut, Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
2. University of Texas at Austin, Austin, Texas 78712, United States
3. Wilhelm
Conrad Röntgen-Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany