1. Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, United States
2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
3. Centre for the Physics of Materials and Department of Physics, McGill University, Montreal PQ H3A 2T8, Canada
4. ICQD/HFNL, University of Science and Technology of China, Hefei, Anhui 230026, China