1. Department of Physics, Shahid Beheshti University, G. C., Evin, Tehran 1983969411, Iran
2. Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
3. Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, 60455-760 Fortaleza, Ceará, Brazil