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CALCULATION OF LIGHT SCATTERING SPECTRA RELATED TO LOW-ENERGY EXCITATION IN LOW-DIMENSIONAL QUANTUM ANTIFERROMAGENTICS SYSTEMS

低维量子反铁磁系统中与低能激发相关的光散射光谱的计算

基本信息

批准号：
12640366
负责人：
NATSUME Yuhei
金额：
$ 2.18万
依托单位：
CHIBA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640366/
关键词：
EXCHANGE SCATTERING MAGNETIC RAMAN SPECTRA SINGLET GRIND STATE QUANTUM ANTIFERROMAGNETS LADDER HEISENBERG SYSTEM TRIPLET DIMERS REPRODUCTION OF SPECTRA EXACT DIAGONALIZATION 梯子構造反強磁性体量子スピン系シングレット基底状態トリプレット対の励起

项目摘要

The low-dimensional antiferromagnetic systems have quite characteristic features. In fact, much work for ground states has been made up to now. On the other hand, optical properties of low-lying excited states on spin-gaps in these systems have been reported by relatively small number of papers. In particular, the magnetic Raman-scattering has been discussed by only a few papers. In the present investigation, we reproduce spectra for the exchange-scattering mechanism in two-leg ladder quantum antiferromagnetic systems by the numerical calculation. We treat the finite Heisenberg ladders, in which legs with antiferromagnetic bonds J_c are connected by rungs with antiferromagnetic, bonds J_r. The calculation is made in the system of 50 x 2 sites with spin=1/2 by the perturbation method for the extension of J_c/J_r, in addition to that in 12 x 2 by the exact diagonalization. The singlet ground states are expressed as the oderings of singlet dimers on rungs for small value of J_c/J_r, while excited states can be described as the patterns for triplet dimers on rungs. In fact, we can make clear the origin of the characteristic shapes of magneitc Raman spectra observe at twice the spin-gaps in C_aV_2O_5. Namely, this asymmetric shape is explained by the fact that the corresponding excited states with large transition moments are composed of patterns of pairs for triplet dimers on adjacent rings. The agreement between the present calculation and the observed spectra is quite well. Furthermore, we investigate magnetic Raman spectra in two-leg ladder systems Sr_<14-x>Ca_xCu_<24>O_<41> with relatively large values of J_c/J_r. By the present analyzes of magnetic Raman spectra in low-dimensional quantum antiferromagnetic systems, we can propose the powerful method for understanding properties of excited states and the origin of spin-gaps.

低维反铁磁系统具有相当独特的特征。事实上，到目前为止，对于基态已经做了很多工作。另一方面，这些系统中自旋间隙上低洼激发态的光学性质已经被相对较少的论文报道。特别是对磁拉曼散射的讨论，文献很少。在本研究中，我们通过数值计算再现了两腿阶梯量子反铁磁系统中交换散射机制的光谱。我们处理有限的海森堡阶梯，其中具有反铁磁键J_c的腿由具有反铁磁键J_r的阶连接。在自旋为1/2的50 × 2位体系中，用微扰法计算了J_c/J_r的扩展，并用精确对角化法计算了12 × 2位体系的扩展。当J_c/J_r值较小时，单重态基态表示为阶上单重态二聚体的阶数，激发态表示为阶上三重态二聚体的模式。事实上，我们可以通过观察C_aV_2O_5中两倍自旋间隙处的磁拉曼光谱特征形状来明确其起源。也就是说，这种不对称的形状可以用这样一个事实来解释：具有大跃迁矩的相应激发态是由相邻环上的三重态二聚体的成对模式组成的。计算结果与实测光谱吻合较好。此外，我们还研究了具有较大J_c/J_r值的双阶梯体系Sr_<14-x>Ca_xCu_<24>O_<41>的磁拉曼光谱。通过对低维量子反铁磁系统的磁性拉曼光谱的分析，我们可以为理解激发态的性质和自旋间隙的起源提供有力的方法。