1. Division of Physics and Applied
Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371,
Singapore
2. Department of
Physics, Southeast University, Nanjing,
211189, China
3. School of Materials
Science and
Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
4. Department of Materials Science
and Engineering, National University of Singapore, Singapore 119260, Singapore