1. Applied Physics Department CINVESTAV, Unidad Mérida Km. 6 Antigua carretera a Progreso Apdo. Postal 73, Cordemex Mérida Yucatán C.P. 97310 Mexico
2. Institute of Physics and Mathematics Universidad Michoacana de San Nicolás de Hidalgo Edificio C-3, Cd. Universitaria Morelia Michoacán C.P. 58040 Mexico
3. CONACYT-Applied Physics Department CINVESTAV, Unidad Mérida Km. 6 Antigua carretera a Progreso Apdo. Postal 73 Cordemex Mérida Yucatán C.P. 97310 Mexico
4. Dipartimento di Scienze di Base e Applicate per l’Ingegneria Sapienza Università di Roma Via Antonio Scarpa 16 00161 Rome Italy