Institution: | a Department of Physics and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan b Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India c Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FI 20014 Turku, Finland |