平面反铁磁体BaNi $_2$ V $_2$ O $_8$中Berezinsky-Kosterlitz-无磁临界行为的特征
Signatures for Berezinsky-Kosterlitz-Thouless critical behaviour in the planar antiferromagnet BaNi$_2$V$_2$O$_8$
摘要：
利用中子衍射和μ子自旋旋转测量研究了自旋$1$蜂窝状反铁磁体BaNi $_2$ V $_2$ O $_8$在有序温度$T_N$以下和之上的临界性质.我们的研究结果表明，BaNi $_2$ V $_2$ O $_8$在整个温度范围内都是二维反铁磁体，随着温度的升高，表现出一系列从二维类伊辛到二维XY再到二维海森堡的交叉行为。特别是，提取的序参量的临界指数揭示了一个狭窄的温度制度接近$T_N$，其中系统的行为作为一个二维XY反铁磁体。在$T_N$以上，从相关长度的标度中得到了涡激发驱动的Berezinsky-Kosterlitz无涡行为的证据.我们的实验结果与对BaNi $_2$ V $_2$ O $_8$微观磁模型哈密顿量的经典和量子蒙特卡罗模拟结果一致.
英文摘要：
We investigate the critical properties of the spin-$1$ honeycomb antiferromagnet BaNi$_2$V$_2$O$_8$, both below and above the ordering temperature $T_N$ using neutron diffraction and muon spin rotation measurements. Our results characterize BaNi$_2$V$_2$O$_8$ as a two-dimensional (2D) antiferromagnet across the entire temperature range, displaying a series of crossovers from 2D Ising-like to 2D XY and then to 2D Heisenberg behavior with increasing temperature. In particular, the extracted critical exponent of the order parameter reveals a narrow temperature regime close to $T_N$, in which the system behaves as a 2D XY antiferromagnet. Above $T_N$, evidence for Berezinsky-Kosterlitz-Thouless behavior driven by vortex excitations is obtained from the scaling of the correlation length. Our experimental results are in accord with classical and quantum Monte Carlo simulations performed for microscopic magnetic model Hamiltonians for BaNi$_2$V$_2$O$_8$.
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