1. a Department of Physics , Fukuoka 812-8581 , Japan
2. b Frontier Research System , The Institute of Physical and Chemical Research (RIKEN) , Hirosawa 2-1, Wako-shi, Saitama 351-0198 , Japan
3. c Center for Theoretical Physics , Physics Department, Center for the Study of Complex Systems , The University of Michigan , Ann Arbor , Michigan 48109-1040 , USA