Pandeya Ram Prakash, Pramanik Arindam, Sakhya Anup Pradhan, Thamizhavel A, Maiti Kalobaran
Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005, India.
J Phys Condens Matter. 2020 May 15;32(33). doi: 10.1088/1361-648X/ab86f0.
Employing high resolution hard x-ray photoemission spectroscopy, we investigate the electronic structure of an exotic Fe-based superconductor, CaFeAs, 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.
利用高分辨率硬X射线光电子能谱，我们研究了一种奇特的铁基超导体CaFeAs的电子结构，该超导体展现出丰富的温度-压力相图，并且在施加压力时实现超导存在二分性。对于不同表面灵敏度的实验，实验价带谱表现出显著差异。我们发现光偏振与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-体相差异。因此，利用芯能级光谱的终态效应来揭示深度分辨信息。在各种芯能级谱中都观察到了与等离子体激元激发相关的强特征。Ca 2p谱显示出与传导电子发生显著杂化的证据，以及对应于表面和体相电子结构的不同特征，而As芯能级则不受影响。不同温度下深度分辨的Fe 2p谱呈现出有趣的特征，表明结构异常可能是一种体相性质。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特性质。
