[1] Univ Tokyo, Dept Appl Phys, Tokyo 1138656, Japan
[2] RIKEN, Adv Sci Inst, CERG, Wako, Saitama 3510198, Japan
[3] Univ Tokyo, Inst Solid State Phys, Kashiwa, Chiba 2278581, Japan
[4] JST, CREST, Tokyo 1020075, Japan
[5] High Energy Accelerator Res Org KEK, Inst Mat Struct Sci, Tsukuba, Ibaraki 3050801, Japan
[6] PRESTO, JST, Kawaguchi, Saitama 3320012, Japan
[7] Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA
[8] Stanford Univ, Stanford Inst Mat & Energy Sci, Stanford, CA 94305 USA