铜酸盐中的共价键和磁性
Covalent bonding and magnetism in cuprates
摘要：
共价键对3d金属配合物磁性的重要性首先由Pauling在1931年指出。然而，随着范弗莱克离子图像的成功，他的观点变得没有实际意义了。在范弗莱克的离子图像中，配体主要通过静电场影响3d离子的磁性电子。安德森的自旋超交换理论后来确立了共价是绝缘体中合作磁性的核心，但其能量尺度被认为与其他离子间相互作用相比很小，因此被认为是离子图像的小扰动。这一论断在铜氧化物中明显失败，铜氧化物在高临界温度超导体（HTSC）发现后才变得突出。铜酸盐中的磁相互作用非常强，通常被认为是异常高的超导转变温度Tc的起源。在这里，我们报告了一个详细的调查磁激发在一维铜酸盐Sr 2CuO 3使用非弹性中子散射（INS）。我们发现，虽然实验的动态自旋结构因子是很好地描述了模型S=1/2最近邻海森堡哈密顿通常用于铜酸盐，修改的磁场强度显着强杂交的Cu 3d状态与O p状态，显示本地化的3d海森堡自旋磁性的离子图片是严重不足。我们的研究结果为铜酸盐中缺失的INS磁场强度之谜提供了一个自然的解释，并对理解这些材料当前和未来的实验数据具有深远的影响。
英文摘要：
The importance of covalent bonding for the magnetism of 3d metal complexes was first noted by Pauling in 1931. His point became moot, however, with the success of the ionic picture of Van Vleck, where ligands influence magnetic electrons of 3d ions mainly through electrostatic fields. Anderson's theory of spin superexchange later established that covalency is at the heart of cooperative magnetism in insulators, but its energy scale was believed to be small compared to other inter-ionic interactions and therefore it was considered a small perturbation of the ionic picture. This assertion fails dramatically in copper oxides, which came to prominence following the discovery of high critical temperature superconductors (HTSC). Magnetic interactions in cuprates are remarkably strong and are often considered the origin of the unusually high superconducting transition temperature, Tc. Here we report a detailed survey of magnetic excitations in the one-dimensional cuprate Sr2CuO3 using inelastic neutron scattering (INS). We show that although the experimental dynamical spin structure factor is well described by the model S=1/2 nearest-neighbour Heisenberg Hamiltonian typically used for cuprates, the magnetic intensity is modified dramatically by strong hybridization of Cu 3d states with O p states, showing that the ionic picture of localized 3d Heisenberg spin magnetism is grossly inadequate. Our findings provide a natural explanation for the puzzle of the missing INS magnetic intensity in cuprates and have profound implications for understanding current and future experimental data on these materials.
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