1. Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashihiroshima, Hiroshima 739-8530
2. Cryogenics and Instrumental Analysis Division, N-BARD, Hiroshima University, Higashihiroshima, Hiroshima 739-8526
3. Institute for Advanced Materials Research, Hiroshima University, Higashihiroshima, Hiroshima 739-8530
4. Institute for Materials Research, Tohoku University, Sendai 980-8577