1. Department of Physics-FFCLRP, University of São Paulo 1 , Ribeirao Preto-SP 14040-901, Brazil
2. Research Unit Condensed Matter, Electronics and Signal Processing, University of Dschang 2 , P.O. Box 67, Dschang, Cameroon
3. MoCLiS Research Group 3 , Dschang, Cameroon
4. Instituto de Física Teórica, São Paulo State University (UNESP) 4 , Rua Dr. Bento Teobaldo Ferraz 271, Bloco II, Barra Funda, 01140-070 São Paulo, Brazil