1. Centro de Física, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020-A, Venezuela
2. KYOKUGEN, Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531
3. Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
4. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195