PHYSICAL REVIEW B, vol. 37, no. 10, page. 5966 - 5969, 1988-04-01
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, vol. 26, page. 1423 - 1424, 1987-01
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, vol. 26, page. 1385 - 1386, 1987-01