The Transition between Haldane Phase and Large-D Phase in S=1/2 Ferro-Antiferro Alternating Spin Chain.

清美 岡本, Kiyomi Okamoto

清美 岡本, Kiyomi Okamoto

Kiyomi Okamoto

We analytically study the ground-state quantum phase transition between the Haldane phase and the large-D (LD) phase of the ferromagnetic - antiferromagnetic alternating Heisenberg chain with on-site anisotropy. We transform this model into a generalized version of the alternating antiferromagnetic Heisenberg model with anisotropy. In the transformed model, the competition between the transverse and longitudinal bond alternations yields the Haldane - LD transition. Using the bosonization method, we show that the critical exponents vary continuously on the Haldane - LD boundary. Our scaling relations between critical exponents explains very well the numerical results of Hida.

Kiyomi Okamoto, Dai Nishino, Yôhei Saika

We analytically study the boundary between the Haldane phase and the large- D (LD) phase of a ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site easy-plane anisotropy. We transform this model into a generalized alternating antiferromagnetic Heisenberg model with anisotropy. In the transformed model, the competition between the transverse and longitudinal alternations results in the Haldane-LD transition. Our Haldane-LD boundary calculated through the bosonization method agrees very well with that of Hida [Phys. Rev. B 46 (1992) 8268], determined by the numerical method.

J. O. de Almeida, Miguel Angel Martin-Delgado, Germán Sierra

We obtain the phase diagram in the parameter space $({J}^{\ensuremath{'}}∕J,\ensuremath{\gamma})$ and an accurate estimate of the critical line separating the different phases. We show several measurements of the magnetization, dimerization, nearest neighbor correlation, and density of energy in the different zones of the phase diagram, as well as a measurement of the string order parameter proposed as the nonvanishing phase order parameter characterizing Haldane phases. All these results will be compared in the limit ${J}^{\ensuremath{'}}∕J⪢1$ with the behavior of the $\mathbf{S}=1$ bond alternated Heisenberg chain (BAHC). The analysis of our data supports the existence of a dimer phase separated by a critical line from a Haldane one, which has exactly the same nature as the Haldane phase in the $\mathbf{S}=1$ BAHC.

S. A. Owerre, Manu B. Paranjape