1. Department of Physics, University of South Florida, Tampa, Florida 33620, USA
2. BCMaterials, Edificio No. 500, Parque Tecnológico de Vizcaya, Derio 48160, Spain
3. Department of Electricity and Electronics, University of Basque Country (UPV/EHU), Leioa 48940, Spain
4. Department of Applied Physics II, University of Basque Country (UPV/EHU), Leioa 48940, Spain