[1] Karlsruhe Inst Technol, Inst Nanotechnol, Inst Condensed Matter Theory, D-76131 Karlsruhe, Germany
[2] Karlsruhe Inst Technol, DFG Ctr Funct Nanostruct, D-76131 Karlsruhe, Germany
[3] Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, D-86135 Augsburg, Germany