1. Physics Department, Federal University of Minas Gerais, Belo HorizonteCEP 31270-901, Brazil
2. Center for High Technology Materials and Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico87131, United States
3. Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas, CampinasCEP 13083-887, Brazil