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arXiv 2103.01455cond-mat.str-el
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类kagome-Heisenberg阶梯中的反常分数量子化:有效自旋-1链的出现

Anomalous fractional quantization in the kagomelike Heisenberg ladder: Emergence of the effective spin-1 chain

Tomoki Yamaguchi, Yukinori Ohta, Satoshi Nishimoto

摘要:

研究了具有竞争铁磁和反铁磁交换作用的类Kagome自旋-$1/2$海森堡阶梯.使用密度矩阵重整化群计算,我们得到的FM和AFM交换相互作用之间的比率的函数的基态相图。存在五个不同的阶段。它们中的三个是自旋极化相; FM相和两种亚铁磁(FR)相(称为FR 1和FR 2相)。每个位点的自发磁化分别为FM、FR 1和FR 2相中的$m=1/2$、$1/3$和$1/6$。这可以从以下事实理解,即由上腿和下腿自旋形成的有效自旋1海森堡链具有每个位点的磁化的三步分数量子化,如$m=1$、$1/2$和$0$。特别是,有效自旋1链的异常"中间"状态$m=1/2$具有从$3$到$2$维度的自旋的约化希尔伯特空间,这在传统自旋1物理学的背景下是非常出乎意料的。因此,令人惊讶的是,有效自旋1链的行为类似于具有SU(2)对称性的自旋1/2链。剩下的两个阶段是自旋单重态阶段与平移对称性破缺的存在下形成价键。一种是八聚体-siglet相,具有系统的自发八聚化长程序;另一种是四周期相,具有四个结构晶胞的周期的磁性超结构。在这些自旋单重态相中,我们发现价键结构和无带隙链共存。虽然这可能是通过有序无序机制出现的,但这种共存的例子很少。

英文摘要:

We study a Kagome-like spin-$1/2$ Heisenberg ladder with competing ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions. Using the density-matrix renormalization group based calculations, we obtain the ground state phase diagram as a function of the ratio between the FM and AFM exchange interactions. Five different phases exist. Three of them are spin polarized phases; an FM phase and two kinds of ferrimagnetic (FR) phases (referred to as FR1 and FR2 phases). The spontaneous magnetization per site is $m=1/2$, $1/3$, and $1/6$ in the FM, FR1, and FR2 phases, respectively. This can be understood from the fact that an effective spin-1 Heisenberg chain formed by the upper and lower leg spins has a three-step fractional quantization of the magnetization per site as $m=1$, $1/2$, and $0$. In particular, an anomalous "intermediate" state $m=1/2$ of the effective spin-1 chain with the reduced Hilbert space of a spin from $3$ to $2$ dimensional is highly unexpected in the context of conventional spin-1 physics. Thus, surprisingly, the effective spin-1 chain behaves like a spin-1/2 chain with SU(2) symmetry. The remaining two phases are spin-singlet phases with translational symmetry breaking in the presence of valence bond formations. One of them is octamer-siglet phase with a spontaneous octamerization long-range order of the system, and the other is period-4 phase characterized by the magnetic superstructure with a period of four structural unit cells. In these spin-singlet phases, we find the coexistence of valence bond structure and gapless chain. Although this may be emerged through the order-by-disorder mechanism, there can be few examples of such a coexistence.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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