1. Department of Physics; Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices; Key Laboratory of Low Dimensional Condensed Matter Physics (Department of Education of Fujian Province); Xiamen University; Xiamen 361005 China
2. Jiujiang Research Institute of Xiamen University; Jiujiang 332000 China
3. Department of Mechanical Engineering and Materials Science; Rice University; Houston TX 77005 USA
4. Tianming Physics Research Institute; Changtai 363900 China