Affiliation: | a Department of Experimental Physics, School of Physics and Engineering Physics, Göteborg University and Chalmers University of Technology, SE-41296, Göteborg, Sweden;b Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296, Göteborg, Sweden;c School of Physics and Condensed Matter Research Institute, Seoul National University, Seoul 151-747, South Korea |