1. Department of Physics, School of Arts & Sciences, Shaanxi University of Science & Technology, Xi’an 710021, China
2. School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332, USA
3. Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Dr NW, Atlanta, GA 30332, USA
4. Nano-Optoelectronics Research Laboratory, Department of Physics, University of Agriculture Faisalabad, Faisalabad 38040, Pakistan