Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China;
School of Physical Sciences University of Chinese Academy of Sciences Beijing 100190 China;
Materials Science and Engineering Program Mechanical Engineering University of Texas at Austin Austin Texas 78712 USA;
Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement of Ministry of Education School of Physics Beijing Institute of Technology Beijing 100081 China;
Department of Physics and Astronomy University of Tennessee Knoxville TN 37996 USA;
School of Physics Georgia Institute of Technology Atlanta GA 30332 USA;
Songshan Lake Materials Laboratory Dongguan 523808 China;
