1. Department of Mathematics and Natural Sciences, BRAC University, Dhaka 1212, Bangladesh
2. Department of Physics, University of Dhaka, Dhaka 1000, Bangladesh
3. Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA
4. The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, I-34014, Trieste, Italy
5. Department of Physics, UAE University, P. O. Box 17551, Al-Ain, United Arab Emirates
6. Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland