1. Department of Physics, Shahjalal University of Science & Technology, Sylhet 3114, Bangladesh
2. Department of Physics, University of Rajshahi, Rajshahi 6205, Bangladesh
3. Department of Physics, Rajshahi University of Engineering & Technology, Rajshahi 6204, Bangladesh
4. School of Computer Science, Carleton University, Ottawa, Ontario K1S 5B6, Canada
5. Department of Physics, Southern Illinois University, Carbondale, IL 62901, USA
6. Department of Physics, Washington University, St. Louis, Mo 63130, USA