Affiliation: | (1) Department of Electronics, Weizmann Institute of Science, Rehovot, Israel;(2) Institut für Theoretische Physik, Universität Frankfurt/Main, Robert-Mayer-Straße 8, D-6000 Frankfurt/Main 1, Federal Republic of Germany;(3) Department of Chemistry, Cornell University, 14853 Ithaca, New York, USA;(4) Present address: Dept. of Physics, Boston University, 02215 Boston, Mass., USA;(5) Institut für Theoretische Physik, Universität, 6600 Saarbrücken, Federal Republic of Germany |