1. Institute of Physics, Sachivalaya Marg, Bhubaneswar-751 005, India
2. School of Physics, Sambalpur University, Jyotivihar, Burla-768 019, India
3. Department of Physics, Indian Institute of Technology, Roorkee 247 667, India
4. Department of Physics, Panjab University, Chandigarh-160 014, India