Employing high resolution hard x-ray photoemission spectroscopy, we investigate the electronic structure of an exotic Fe-based superconductor, CaFe2As2, which exhibits rich temperature pressure phase diagram and dichotomy on achieving superconductivity on application of pressure. The experimental valence band spectra exhibit significant differences for experiments at different surface sensitivities. We discover that the change in angle between light polarization and surface normal leads to similar orbital selective spectral response suggesting requirement of different methodology to probe the surface-bulk differences. Thus, the final state effects of the core level spectroscopy has been exploited to reveal the depth-resolved information. Strong features related to plasmon excitations have been observed in various core level spectra. Ca 2p spectra exhibit evidence of significant hybridization with the conduction electrons, and distinct features corresponding to the surface and bulk electronic structures while As core levels remain unaffected. The depth-resolved Fe 2p spectra at different temperatures exhibit interesting features suggesting structural anomaly may be a bulk property. All these results reveal complexity in the hybridization physics between Fe, As and Ca states presumably leading to exoticity in this material.

中文翻译：

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CaFe2As2 中的复杂杂化物理——高分辨率硬 X 射线光电子研究


采用高分辨率硬X射线光电子能谱，我们研究了一种奇异的铁基超导体CaFe2As2的电子结构，它表现出丰富的温度压力相图和在压力应用下实现超导性的二分法。不同表面灵敏度下的实验价带光谱表现出显着差异。我们发现光偏振和表面法线之间角度的变化会导致类似的轨道选择性光谱响应，这表明需要不同的方法来探测表面体差异。因此，核心能级光谱的最终状态效应被用来揭示深度分辨信息。在各种核心能级光谱中观察到与等离激元激发相关的强烈特征。 Ca 2p 光谱显示出与传导电子显着杂化的证据，以及与表面和体电子结构相对应的明显特征，而 As 核心水平不受影响。不同温度下的深度分辨 Fe 2p 光谱表现出有趣的特征，表明结构异常可能是一种整体特性。所有这些结果揭示了 Fe、As 和 Ca 态之间杂化物理的复杂性，这可能导致了这种材料的奇异性。