1. Texas Center for Superconductivity, University of Houston, Houston, TX 77204, USA
2. Instituto de Investigaciones en Materiales, UNAM, 04510 México DF, Mexico
3. Consortium of the Americas for Interdisiplinary Science, University of New Mexico, Albuquerque, NM 87131, USA
4. Instituto de Física, UNAM, 01000 México, DF, Mexico