Polarization dependence of x-ray absorption spectra ofNaxCoO2: Electronic structure from cluster calculations
Polarization dependence of x-ray absorption spectra ofNaxCoO2: Electronic structure from cluster calculations
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DOI：
10.1103/physrevb.74.115124
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发表时间：
2006-09
影响因子：
3.7
通讯作者：
T. Kroll;A. Aligia;G. Sawatzky
中科院分区：
文献类型：
--
作者：
T. Kroll;A. Aligia;G. Sawatzky
为了揭示Na_xCoO_2的电子结构，在最近Co L边X射线吸收光谱（XAS）实验的激发下，我们计算了CoO_6团簇的电子光谱，包括了3d轨道间的所有相互作用.我们得到了团簇中两个电子占据的基态，它们名义上对应于O^{-2}氧化态的所有O，以及Co^{+3}或Co^{+4}。然后，所有的激发态得到的促进Co 2 p电子的3d电子，和相应的矩阵元素进行了计算。所观察到的实验光谱的拟合是好的，并指出一个大的Co-O共价和立方晶场效应，导致低自旋Co 3d配置。我们的结果表明，不同的Co原子之间的有效跳跃起着重要的作用，在确定晶格中的基态的对称性。剩余的定量差异与XAS实验预计来自组成的影响，在地面和激发态的巡回。
In order to shed light on the electronic structure of Na_xCoO_2, and motivated by recent Co L-edge X-ray absorption spectra (XAS) experiments with polarized light, we calculate the electronic spectrum of a CoO_6 cluster including all interactions between 3d orbitals. We obtain the ground state for two electronic occupations in the cluster that correspond nominally to all O in the O^{-2} oxidation state, and Co^{+3} or Co^{+4}. Then, all excited states obtained by promotion of a Co 2p electron to a 3d electron, and the corresponding matrix elements are calculated. A fit of the observed experimental spectra is good and points out a large Co-O covalency and cubic crystal field effects, that result in low spin Co 3d configurations. Our results indicate that the effective hopping between different Co atoms plays a major role in determining the symmetry of the ground state in the lattice. Remaining quantitative discrepancies with the XAS experiments are expected to come from composition effects of itineracy in the ground and excited states.