JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, vol. 36, no. 4A, page. 2134 - 2135, 1997-04
PHYSICAL REVIEW LETTERS, vol. 82, no. 3, page. 536 - 539, 1999-01-18
INSTITUTE OF PHYSICS CONFERENCE SERIES, no. 162, page. 73 - 78, 1999-01