1. I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
2. Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
3. Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan.