Affiliation: | a Department of Physics and Measurement Technology, Linköping University, S-581 83, Linköping, Sweden b NTT Opto-electronics Lab, 3-1 Morinosato, Atsugi, Kanagawa 243 01, Japan c High Magnetic Field Laboratory, Max-Planck-Institut für Festkörperforschung and CNRS, F-38042, Grenoble, France |