Finite-Field Ground State of the S=1 Antiferromagnetic-Ferromagnetic Bond-Alternating Chain

清美 岡本, Kiyomi Okamoto

Takashi Tonegawa, Kiyomi Okamoto, Makoto Kaburagi

We investigate the finite-field ground state of the S=1 antiferromagnetic-ferromagnetic bond-alternating chain described by the Hamiltonian ${\calH}=\sum\nolimits_{\ell}\bigl\{\vecS_{2\ell-1}\cdot\vecS_{2\ell} +J\vecS_{2\ell}\cdot\vecS_{2\ell+1}\bigr\} +D\sum\nolimits_{\ell} \bigl(S_{\ell}^z)^2 -H\textstyle\sum\nolimits_\ell S_\ell^z$, where \hbox{$J\leq0$} and \hbox{$-\infty

Tôru Sakai

Kazuo Hida

The ground state of the ferromagnetic-antiferromagnetic alternating spin-1/2 Heisenberg chain is studied with Ising-type anisotropy on the ferromagnetic bond. This model tends to the spin-1 antiferromagnetic Heisenberg chain with on-site anisotropy in the limit of strong ferromagnetic bond. It is found that the Haldane-gap phase, the large-D phase, and the two types of N\'eel phases appear as the ground state of this model. The duality relations between these four phases are proved for several limiting cases. The string order parameter characterizing the large-D phase is introduced based on these duality relations. The ground-state phase diagram is determined by the numerical diagonalization of the finite-size system.

Kazuo Hida

The ground state of the alternating spin-1/2 Heisenberg chain is studied with anisotropy on the antiferromagnetic bond. This model reduces to the spin-1 XXZ chain if the isotropic bond is ferromagnetic and infinitely strong. The ground-state phase diagram is determined by the numerical diagonalization of finite-size systems. The results are consistent with the series expansion results by Yamanaka, Hatsugai and Kohmoto, and confirms the qualitative phase diagram predicted by Kohmoto and Tasaki.

Takashi Tonegawa, Takashi Hikihara, Kazuki Okamoto +1 more