Study of the ground state of 4f electrons near a quantum critical point by means of "soft x-ray absorption spectroscopy" under pressure

M边和N边的x射线吸收光谱（XAS）是检测4f电子的价态、空间对称性和杂化的有力工具。然而，由于软x射线的穿透深度短，该技术不适用于压力下的测量。x射线拉曼光谱（XRS）是利用硬x射线获得XAS光谱的一种替代方法。因此，我们进行了XRS的可行性研究，并证实了XRS是观察压力下f电子基态的潜在工具。然而，与此同时，我们发现XRS并不完全等同于XAS，这一结果指出，必须特别注意XRS数据的解释。

X-ray absorption spectroscopy(XAS) at M and N edges is a powerful tool that can detect valency, spatial symmetry and hybridization of 4f electrons. However, this technique is not applicable for measurements under pressure, because of short penetration depth of soft x-rays. X-ray Raman spectroscopy(XRS) is an alternative method to obtain XAS spectra using hard x-rays. We therefore carried out feasibility study of XRS and confirmed that XRS is a potential tool for observing the electronic ground states of f-electrons under pressure. At the same time, however, we found that XRS is not perfectly equivalent to XAS and this result points out that particular care must be taken for the interpretation of XRS data.