1. KYOKUGEN, Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531
2. Département de Physique de la Matière Condensée, Section de Physique, University of Geneva, 24 quai Ernest-Ansermet CH-1211 Genève 4, Switzerland
3. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531