arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0705.0263cond-mat.str-el
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间接共振非弹性X射线散射研究La2CuO4的磁激发

Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering

Filomena Forte, Luuk J. P. Ament, Jeroen van den Brink

摘要:

最近的实验表明,间接共振非弹性X射线散射(RIXS)可能提供一个探针的横向自旋动力学的La $_2$ CuO $_4$。我们详细介绍了一个系统的扩展相关的磁RIXS截面使用超短芯孔寿命(UCL)近似。我们计算了UCL展开式的首阶散射强度及其动量依赖关系。散射是由于两个磁振子的过程,并计算内的线性自旋波扩展的海森堡自旋模型为这种化合物,包括更长的范围和循环自旋相互作用。我们观察到,后面的条款中的哈密顿增强的第一时刻的频谱,如果他们加强反铁磁有序。理论谱与实验数据吻合得很好,包括观察到转移动量${\bf q} = (0,0)$和${\bf q} = (π,π)$的散射强度为零。我们表明,在有限的温度下,有一个额外的单磁振子的散射贡献与$T^3$的光谱权重成正比。我们还计算了UCL近似的主要修正,发现它们很小,从而为UCL结果奠定了坚实的基础。所有这一切都明确地指出,在La $_2$ CuO $_4$中观察到的低温RIXS强度是由于双磁振子散射。

英文摘要:

Recent experiments on La$_2$CuO$_4$ suggest that indirect resonant inelastic X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We present in detail a systematic expansion of the relevant magnetic RIXS cross section by using the ultrashort core-hole lifetime (UCL) approximation. We compute the scattering intensity and its momentum dependence in leading order of the UCL expansion. The scattering is due to two-magnon processes and is calculated within a linear spin-wave expansion of the Heisenberg spin model for this compound, including longer range and cyclic spin interactions. We observe that the latter terms in the Hamiltonian enhance the first moment of the spectrum if they strengthen the antiferromagnetic ordering. The theoretical spectra agree very well with experimental data, including the observation that scattering intensity vanishes for the transferred momenta ${\bf q} = (0,0)$ and ${\bf q} = (π,π)$. We show that at finite temperature there is an additional single-magnon contribution to the scattering with a spectral weight proportional to $T^3$. We also compute the leading corrections to the UCL approximation and find them to be small, putting the UCL results on a solid basis. All this univocally points to the conclusion that the observed low temperature RIXS intensity in La$_2$CuO$_4$ is due to two-magnon scattering.

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