Two-magnon Raman scattering in insulating cuprates: Modifications of the effective Raman operator
Two-magnon Raman scattering in insulating cuprates: Modifications of the effective Raman operator
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绝缘铜酸盐中的双磁振子拉曼散射：有效拉曼算子的修改
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
R. Singh
中科院分区：
文献类型：
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作者：
P. J. Freitas;R. Singh
用Fleury-Loudon-Elliott理论计算自旋为1/2的正方晶格Heisenberg模型中的拉曼散射强度，迄今为止还不能描述实验上在铜酸盐材料中发现的两个磁振子峰的宽线形和不对称性。更值得注意的是，相对于Fleury-Loudon-Elliott理论，极化选择规则被违反。在$B_{1g}$和$A_{1g}$中存在类似的散射，而理论只预言了$B_{1g}$中的散射。我们回顾了这种差异的各种建议，并建议至少部分问题可以通过修改有效的拉曼哈密顿量，允许任意总动量的两个磁振子状态来解决。这种基于Sawatzsky-Lorenzana光学吸收理论的方法假设声子作为动量汇的重要作用。它保持了海森堡模型的低能物理不变，但大大改变了拉曼线的形状和选择规则，使结果更接近实验。
Calculations of Raman scattering intensities in spin 1/2 square-lattice Heisenberg model, using the Fleury-Loudon-Elliott theory, have so far been unable to describe the broad line shape and asymmetry of the two magnon peak found experimentally in the cuprate materials. Even more notably, the polarization selection rules are violated with respect to the Fleury-Loudon-Elliott theory. There is comparable scattering in $B_{1g}$ and $A_{1g}$ geometries, whereas the theory would predict scattering in only $B_{1g}$ geometry. We review various suggestions for this discrepency and suggest that at least part of the problem can be addressed by modifying the effective Raman Hamiltonian, allowing for two-magnon states with arbitrary total momentum. Such an approach based on the Sawatzsky-Lorenzana theory of optical absorption assumes an important role of phonons as momentum sinks. It leaves the low energy physics of the Heisenberg model unchanged but substantially alters the Raman line-shape and selection rules, bringing the results closer to experiments.