Theoretical Studies on Many-Body Effects in Core Spectroscopies by Nonequilibrium Green 's Functions

本文应用Keldysh的非平衡绿色函数，发展了X射线光电子衍射（XPD）谱的多体理论，该理论基本上是由Caroli等人应用的，我们应用了以修饰单电子绿色函数G和屏蔽库仑相互作用W表示的骨架图展开。在光学势影响下的阻尼光电子波函数在当前XPD理论中发挥着核心作用。在此基础上，详细讨论了有限温度下XPD谱中的Debye-Waller因子和Franck-Condon因子、共振效应特别是多原子共振光电子能谱（MARPE）效应以及损耗效应。XPD光谱由Franck-Condon因子和包括Debye-Waller因子的XPD强度的乘积简单地描述。该结果与XAFS相反，其中Franck-Condon因子被卷积乘积模糊。我们已经讨论了产生突出的MARPE光谱的条件。特别是对称性降低起着重要的作用，产生突出的MARPE光谱。角依赖性为我们提供了近邻原子排列的有用信息。一些模型计算阐明了MARPE谱的基本物理过程。为了讨论损耗谱，我们强调了本征损耗和非本征损耗之间干涉效应的重要性。在本文的理论框架下，导出了包含非弹性散射和弹性散射的显式公式。这些公式使我们能够计算与损失相关的XPD模式。我们还发现了辐射场筛选的重要性，以描述特别是MARPE的共振效应。随着量子电动力学（QED）理论的实现，XPS和X射线吸收谱中包含光场效应的项目也在不断发展。

Many-body theory of X-ray photoelectron diffraction(XPD) spectra is developed by using Keldysh's nonequilibrium Green's functions, which was basically applied by Caroli et al. We have applied skeleton diagram expansion in terms of dressed one-electron Green's function G and the screened Coulomb interaction W. The damping photoelectron wave functions under the influence of the optical potential play a central role of the present XPD theory. Based on the present theoretical framework, we give detailed discussion on Debye-Waller and Franck-Condon factors in XPD spectra at finite temperature, resonance effects in particular multi atom resonant photoemission(MARPE) effects, and also on the loss effects. The XPD spectra is simply described by a product of the Franck-Condon factor and the XPD intensity including the Debye-Waller factor. This result is contrast to the XAFS where the Franck-Condon factor is smeared out by a convolution product. We have discussed the conditions which give rise to prominent MARPE spectra. In particular symmetry lowering plays an important role to give rise to prominent MARPE spectra. The angular dependence provides us useful information on near neighbor atomic arrangement. Some model calculations clarify the basic physical processes of MARPE spectra. To discuss the loss spectra, we stress the importance of the interference effects between the intrinsic and extrinsic losses. The explicit formulas which include both inelastic and elastic scatterings are newly derived in the present theoretical framework. These formulas enable us to calculate XPD pattern associated with losses. We also have found the importance of the radiation field screening to describe the resonance effects in particular MARPE. As we realized the quantum electrodynamic(QED) theory, the project to include optical field effects in XPS and X-ray absorption spectra.