Applied Materials Physics Group, Department of Materials Science and Engineering, The Royal Institute of Technology, Brinellvagen 23, Stockholm, 100 44 Sweden
Condensed Matter Theory Group, Department of Physics, Uppsala University, Box 530, Uppsala, 751 21 Sweden
Applied Materials Physics Group, Department of Materials Science and Engineering, The Royal Institute of Technology, Brinellvagen 23, Stockholm, 100 44 Sweden ; Condensed Matter Theory Group, Department of Physics, Uppsala University, Box 530, Uppsala, 751 21 Sweden