1. Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, China
2. School of Physics, Institute for Research in Fundamental Sciences (IPM), Tehran 19395-5531, Iran
3. Department of Physics, University of Guilan, P.O. Box 41335-1914, Rasht 32504550, Iran