S = 1/2 Trimerized XXZ 鎖の磁化プラトー

清美 岡本, 充弘 北沢

Chengkang Zhou, Yuanwei Feng, Jiawei Ruan +1 more

We consider the triangular kagome XXZ-Ising model (TKL XXZ-Ising model) formed by inserting small triangles ("a-trimers") with XXZ spin-1 inside the triangles of the kagome lattice ("b-trimers"). It is a mixed spin system and can be solved exactly by transforming into the kagome lattice with the general transformation method for decorated spin systems. In the absence of an external field, we integrate out the quantum spins of the a-trimers and map the TKL model to the kagome Ising model exactly. We obtain the full phase diagram and their zero-temperature entropies (e.g., s_{max}=5.48895 per unit cell is given for the phase with the maximum entropy). When an external field is applied, 20 phases are found due to the quantum fluctuations of a-trimers. Moreover, the high spins in the a-trimers can lead to a stable quantized growth of the magnetization process in the Heisenberg limit.

Kiyomi Okamoto, Atsuhiro Kitazawa

Kiyomi Okamoto, Atsuhiro Kitazawa

We study the plateau of the magnetization curve at M = M s /3 ( M s is the saturation magnetization) of the S = ½ trimerized XXZ spin chain. By examining the level crossing of low-lying excitations obtained from the numerical diagonalization, we precisely determine the phase boundary between the plateau state and the no-plateau state on the - t plane, where denotes the XXZ anisotropy and t the magnitude of the trimerization. This quantum phase transition is of the Berezinskii-Kosterlitz-Thouless type.

Keigo Hijii, Atsuhiro Kitazawa, K. Nomura

Kiyomi Okamoto