1. Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11793, USA.
2. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA.
3. Department of Physics, Sogang University, Seoul 04107, Korea.
4. Department of Physics and POSTECH Photon Science Center, Pohang University of Science and Technology, Pohang 37673, Korea.
5. Pohang Accelerator Laboratory, Pohang, Gyeongbuk 37673, Korea.
6. Computational Science Initiative, Brookhaven National Laboratory, Upton, NY 11793, USA.
7. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11793, USA.
8. London Centre for Nanotechnology, University College London, London WC1E 6BT, UK.