Resonating valence bond theory of anomalous spin dynamics of spin-1/2 triangular lattice Heisenberg antiferromagnet and its application to Ba3CoSb2O9
Resonating valence bond theory of anomalous spin dynamics of spin-1/2 triangular lattice Heisenberg antiferromagnet and its application to Ba3CoSb2O9
复制标题
自旋1/2三角晶格海森堡反铁磁体反常自旋动力学的共振价键理论及其在Ba3CoSb2O9中的应用
DOI：
10.1103/physrevb.102.075108
复制
发表时间：
2020
影响因子：
3.7
通讯作者：
Li Tao
中科院分区：
文献类型：
--
作者：
Zhang Chun;Li Tao
尽管人们普遍认为自旋三角晶格海森堡反铁磁体（TLHAF）具有长程有序基态，但仍缺乏对其自旋动力学的透彻理解。虽然线性自旋波理论 (LSWT) 预测磁布里渊区 (MBZ) 中磁振子模的三个分支，但发现下一阶的膨胀在以该点为中心的 MBZ 的大部分区域中被破坏，从而使磁振子模的命运未定。最近的中子散射测量（自旋 TLHAF 的理想实现）为这个问题提供了令人惊讶的答案。在该点周围观察到磁振子模式的两个而不是三个分支，其色散相对于 LSWT 预测进行了强烈的重整化，并在该点处表现出明显的类旋子最小值。这伴随着较高能量下的强自旋涨落连续体，其中观察到两个来源不明的强而宽的光谱峰。在这项工作中，我们通过在系统基态的描述中调用共振价键（RVB）物理原理，提出了这些光谱异常的简单图像。我们发现磁振子色散中的类旋子极小值可以通过集体自旋涨落与在a通量背景下运动的狄拉克自旋子激发连续体之间的耦合来解释。我们还提出连续体中的两个宽峰可以分别理解为朗道阻尼第三磁振子模式和朗道阻尼纵向模式。这样的图片可以通过研究各种光谱特征的偏振特性来验证。
Although it is well accepted that the spin-triangular lattice Heisenberg antiferromagnet (TLHAF) has a long-range ordered ground state, a thorough understanding of its spin dynamics is still missing. While the linear spin wave theory (LSWT) predicts three branches of magnon mode in the magnetic Brillouin zone (MBZ), theexpansion at the next order is found to break down in a large portion of the MBZ centered around thepoint, leaving the fate of the magnon modes there undecided. Recent neutron scattering measurement on, an ideal realization of the spin-TLHAF, provides a surprising answer to this issue. Two, rather than three branches, of magnon mode are observed around thepoint, whose dispersion is strongly renormalized with respect to the LSWT prediction and exhibit pronounced rotonlike minimum at thepoint. This is accompanied by a strong spin fluctuation continuum at higher energy, inside which two strong and broad spectral peaks of unknown origin are observed. In this work, we propose a simple picture for these spectral anomalies by invoking the resonating valence bond (RVB) physics in the description of the ground state of the system. We find that the rotonlike minimum in the magnon dispersion can be explained by the coupling between the collective spin fluctuation and the continuum of Dirac spinon excitation moving in a-flux background. We also propose that the two broad peaks in the continuum can be understood respectively as the Landau damped third magnon mode and the Landau damped longitudinal mode. Such a picture can be verified by studying the polarization character of the various spectral features.