1. Department of Physics, National University of Singapore, Singapore 117542, Singapore
2. Institute for Theoretical Physics Amsterdam and Delta Institute for Theoretical Physics, University of Amsterdam, Amsterdam 1098XH, The Netherlands
3. Department of Physics, Indian Institute of Science, Bangalore 560012, India
4. Joint School of National University of Singapore and Tianjin University, Binhai New City, Fuzhou 350207, China
5. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
6. Institute of Materials Research & Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore