1. Institutes of Physical Science and Information Technology Anhui University Hefei Anhui 230601 People's Republic of China
2. Stony Brook Institute at Anhui University Anhui University Hefei Anhui 230039 People's Republic of China
3. School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore
4. School of Electrical and Electronic Engineering Nanyang Technological University Singapore 639798 Singapore
5. Department of Physics Indiana University, Bloomington IN 47405 USA
6. MESA+ Institute for Nanotechnology University of Twente 7500 AE Enschede The Netherlands