PHYSICAL REVIEW B, vol. 65, no. 23, 2002-06-15
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, vol. 45, no. 3, page. 652 - 655, 2004-09
INTERNATIONAL JOURNAL OF MODERN PHYSICS B, vol. 19, no. 1-3, page. 281 - 284, 2005-01-30