Competition between the Bond Alternation and the Anisotropy in Spin-1/2 XY Chain

清美 岡本, Kiyomi Okamoto

Oleg Derzhko, Taras Verkholyak, Taras Krokhmalskii +1 more

清美 岡本, Kiyomi Okamoto

Tôru Sakai, Masaru Hashimoto, Tomoki Houda +4 more

Kiyomi Okamoto, Kaoru Yasumura

We investigate the ground state of the alternating spin-1/2 XY chain with the anisotropy H = J ∑ i [1+(-1) i δ][(1+γ) S i x S i +1 x +(1-γ) S i y S i +1 y ], J >0, where 0≤γ≤1 and 0≤δ≤1. From the exact results of the ground state energy calculation, the ground state is found to be either one of the following three states: the spin fluid state (γ=δ=0), the effective singlet pair state (ES state; δ>γ) and the Néel state (γ>δ). We also exactly calculate the asymptotic form of the longitudinal spin correlation < S i z S j z > in the long distance limit. Both its functional form and the parameter dependence of the correlation length are quite consistent with our picture for the ES state and the Néel state.

김종재

The thermodynamic properties of a trimeric S=1/2 XY spin chain, where unit cells of the ferro-antiferro-antiferromagnetic interaction bonds are displaced alternately, is calculated analytically by using the Jordan-Wigner fermionic transformation. The anisotropy in the coupling bonds causes some unusual characteristics in the specific heat, the magnetization, and the magnetic susceptibility.