1. School of Mechanical and Automotive EngineeringSouth China University of Technology Guangzhou 510640 China
2. Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum MaterialsAcademy of Advanced OptoelectronicsSouth China Normal University Guangzhou 510006 China
3. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper DisplaysSouth China Academy of Advanced OptoelectronicsSouth China Normal University Guangzhou 510006 China
4. Laboratory of Solid State MicrostructuresNanjing University Nanjing 210093 China
5. Department of PhysicsBoston CollegeChestnut Hill MA 02467 USA