1. Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana, Illinois USA
2. Department of Physics, Chemistry, and Pharmacy; University of Southern Denmark, Campusvej 55; DK-5230 Odense M Denmark
3. On leave from A.F. Ioffe Physical-Technical Institute; St. Petersburg Russia
4. Frankfurt Institute for Advanced Studies; Goethe University; Frankfurt am Main Germany
5. Laboratoire Aimé Cotton CNRS II; Université Paris-Sud; 91405 Orsay Cedex France