1. College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-Optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
2. Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
3. School of Physics and Electronics, Hunan University, Changsha, Hunan 410082, China