标题： 自旋-1/2 kagome 反铁磁体中 1/3 磁化平台的性质 显示英文标题

标题： Nature of the 1/3 Magnetization Plateau in Spin-1/2 Kagome Antiferromagnets

摘要： 我们研究了1/3磁化平台的起源，针对$S=1/2$Kagome反铁磁海森堡模型，使用变分蒙特卡洛方法和精确对角化方法，以解释最近在YCu$_3$(OH)$_{6+x}$Br$_{3-x}$和YCu$_3$(OD)$_{6+x}$Br$_{3-x}$中的实验观测结果。 我们确定了三种退化的价键固体（VBS）态，它们构成了一个 $\sqrt{3} \times \sqrt{3}$ 原胞。这些态在自旋磁矩分布中表现出大卫星图案，仅有两个分数值 $-1/3$ 和 $2/3$，并且通过平移变换相互关联。虽然这些VBS态中的自旋关联被发现为短程的，类似于量子自旋液体，但我们表明它们具有消失的拓扑纠缠熵，因此是拓扑平凡的多体态。我们的理论结果提供了有力的证据，表明最近实验中观察到的1/3磁化平台来自具有分数自旋磁矩的 $\sqrt{3} \times \sqrt{3}$ VBS态。 显示英文摘要

摘要： We investigate the origin of the 1/3 magnetization plateau in the $S=1/2$ kagome antiferromagnetic Heisenberg model using the variational Monte Carlo and exact diagonalization methods, to account for the recent experimental observations in YCu$_3$(OH)$_{6+x}$Br$_{3-x}$ and YCu$_3$(OD)$_{6+x}$Br$_{3-x}$. We identify three degenerate valence-bond-solid (VBS) states forming a $\sqrt{3} \times \sqrt{3}$ unit cell. These states exhibit David-star patterns in the spin moment distribution with only two fractional values $-1/3$ and $2/3$, and are related through translational transformations. While the spin correlations in these VBS states are found to be short-range, resembling a quantum spin liquid, we show that they have a vanishing topological entanglement entropy and thus are topologically trivial many-body states. Our theoretical results provide strong evidence that the 1/3 magnetization plateau observed in recent experiments arises from these $\sqrt{3} \times \sqrt{3}$ VBS states with fractional spin moments.