1. Solid
State Physics/The Nanometer Structure Consortium, Lund University, Box 118, SE-221 00 Lund, Sweden
2. Department
of Mathematics, Physics and Electrical Engineering, Halmstad University, Box 823, SE-301 18, Halmstad, Sweden
3. Institute
for Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz
1, D-07743 Jena, Germany
4. Department
of Physics and Electrical Engineering, Linneaus University, SE-39233 Kalmar, Sweden
5. Institute
of Physics, Academia Sinica, Taipei, Taiwan
6. Department
of Physics, National Donghwa University, Taiwan