Affiliation: | (1) Department of Materials Science, The Ångström Laboratory, Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden;(2) Institute of Solid State Physics, University of Latvia, Kengaraga 8, 1063 Riga, Latvia;(3) Physics and Engineering Physics, Chalmers University of Technology and Göteborg University, SE-412 96 Gothenburg, Sweden |