以V $_2$ O $_3$为例说明的过渡金属X射线吸收K前边缘处的原子和巡回效应
Atomic and itinerant effects at the transition metal x-ray absorption K-pre-edge exemplified in the case of V$_2$O$_3$
摘要：
X射线吸收光谱法是一种用于获得过渡金属和稀土化合物中轨道和自旋自由度信息的成熟工具。为此目的，通常采用L-（2 p到3d）和M-（3d到4f）边的偶极跃迁，而在这方面很少研究更高阶的跃迁，如K边的四极1 s到3d。这是由于这样的事实，通常这样的四极跃迁被偶极允许的1 s到4p跃迁所掩盖，因此，在边缘前区域中仅作为次要特征可见。尽管如此，这些特征携带了许多有价值的信息，类似于偶极L边跃迁，由于金刚石砧压室的吸收，在压力下的实验中无法获得。最近，我们进行了理论和实验分析，这种情况下的金属绝缘体转变的（V（1-x）Crx）2 O3。由于轨道自由度在这种跃迁中的重要性被广泛接受，因此对钒K前边缘的四极跃迁的透彻理解提供了有关基础物理的关键信息。此外，在钒站点的反转对称性的缺乏导致钒3d-和4p-状态的现场混合以及偶极和四极跃迁之间的相关量子力学干扰。在这里，我们提出了一个理论分析的实验高分辨率X射线吸收光谱在V前K边缘测量的部分荧光产额模式的单晶。我们进行了密度泛函以及组态相互作用的计算，以捕捉来自两个，巡回和原子限制的影响。
英文摘要：
X-ray absorption spectroscopy is a well established tool for obtaining information about orbital and spin degrees of freedom in transition metal- and rare earth-compounds. For this purpose usually the dipole transitions of the L- (2p to 3d) and M- (3d to 4f) edges are employed, whereas higher order transitions such as quadrupolar 1s to 3d in the K-edge are rarely studied in that respect. This is due to the fact that usually such quadrupolar transitions are overshadowed by dipole allowed 1s to 4p transitions and, hence, are visible only as minor features in the pre-edge region. Nonetheless, these features carry a lot of valuable information, similar to the dipole L-edge transition, which is not accessible in experiments under pressure due to the absorption of the diamond anvil pressurecell. We recently performed a theoretical and experimental analysis of such a situation for the metal insulator transition of (V(1-x)Crx)2O3. Since the importance of the orbital degrees of freedom in this transition is widely accepted, a thorough understanding of quadrupole transitions of the vanadium K-pre-edge provides crucial information about the underlying physics. Moreover, the lack of inversion symetry at the vanadium site leads to onsite mixing of vanadium 3d- and 4p- states and related quantum mechanical interferences between dipole and quadrupole transitions. Here we present a theoretical analysis of experimental high resolution x-ray absorption spectroscopy at the V pre-K edge measured in partial fluorescence yield mode for single crystals. We carried out density functional as well as configuration interaction calculations in order to capture effects coming from both, itinerant and atomic limits.
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