フルヤ　シュンスケ   FURUYA Shunsuke   古谷　峻介    所属   埼玉医科大学  医学部 教養教育    職種   専任講師
論文種別	学術雑誌(原著)
言語種別	英語
査読の有無	査読あり
表題	Anomalous behavior of the spin gap of a spin-1/2 two-leg antiferromagnetic ladder with Ising-like rung interactions
掲載誌名	正式名：PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS ISSNコード：0370-1972
出版社	WILEY-V C H VERLAG GMBH
巻・号・頁	250(3),575-578頁
著者・共著者	Takashi Tonegawa,Kiyomi Okamoto,Shunsuke C. Furuya,Toru Sakai
発行年月	2013/03
概要	Using mainly numerical methods, we investigate the width of the spin gap of a spin-1/2 two-leg ladder described by ${\cal H} = J_{ { \rm l } } \sum\nolimits_{j = 1}<^>{N/2} {} [{\bf S}_{j,a} \cdot {\bf S}_{j + 1,a} + {\bf S}_{j,b} \cdot {\bf S}_{j + 1,b} ] + J_{ { \rm r } } \sum\nolimits_{j = 1}<^>{N/2} {} [\lambda (S_{j,a}<^>{x} S_{j,b}<^>{x} + S_{j,a}<^>{y} S_{j,b}<^>{y} ) + S_{j,a}<^>{z} S_{j,b}<^>{z} ]$, where $S_{j,a(b)}<^>{\alpha } $ denotes the -component of the spin-1/2 operator at the j-th site of the a (b) chain. We mainly focus on the $J_{ { \rm r } }$ >> $J_{ { \rm l } } > 0$ and $|\lambda |\ll 1$ case. The width of the spin gap between the M=0 and 1 subspaces (M is the total magnetization) as a function of anomalously increases near =0; for instance, for $- 0.1 $ less than or similar to $\lambda$ less than or similar to $0.1$ when Jl/Jr=0.1. The gap formation mechanism is thought to be different for the <0 and >0 cases. Since, in usual cases, the width of the gap becomes zero or small at the point where the gap formation mechanism changes, the above gap-increasing phenomenon in the present case is anomalous. We explain the origin of this anomalous phenomenon by use of the degenerate perturbation theory. We also draw the ground-state phase diagram.
DOI	10.1002/pssb.201200757
arXiv ID	arXiv:1211.5764
PermalinkURL	http://arxiv.org/abs/1211.5764v2