Affiliation: | (1) Centre for Advanced Study, Drammensveien 78, N-0271 Oslo, Norway;(2) Department of Physics, University of Oslo, P.O. Box 1048, N-0316 Oslo, Norway;(3) Division of Solid State Physics, Ioffe Institute of the Russian Academy of Sciences, St. Petersburg, 194021, Russia;(4) Division of Solid State Theory, Department of Physics, Lund University, Sölvegatan 14A, S-22362 Lund, Sweden |