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arXiv 2011.05400cond-mat.str-el
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共振非弹性X射线散射谱中电子-声子耦合效应的单点近似模型

Beyond the single-site approximation modeling of electron-phonon coupling effects on resonant inelastic X-ray scattering spectra

Krzysztof Bieniasz, Steven Johnston, Mona Berciu

摘要:

共振非弹性X射线散射(RIXS)越来越多地用于表征材料中的低能集体激发。RIXS是一种强大的探测器,通常需要复杂的理论描述来解释数据。特别是,需要准确的理论描述的影响,电子-声子($e$ -p)耦合RIXS光谱正变得及时,仪器分辨率提高,这种能量制度正在迅速成为可访问的。到目前为止,只有相当探索性的理论工作已经进行了这样的问题。我们开始弥合这一差距,提出了一个通用的变分近似计算RIXS光谱在弱掺杂材料,各种型号与不同的$e$ -p耦合。在这里,我们通过研究电子迁移率的作用来说明它的一些潜力,电子迁移率在基于Lang-Firsov理论的广泛使用的局部近似中完全被忽略。假设电子-声子耦合是最简单的Holstein型,我们讨论了局域近似失效的区域,并证明了局域近似的不当使用会严重影响\textit{underestimate}的$e$ -p耦合强度.

英文摘要:

Resonant inelastic X-ray scattering (RIXS) is used increasingly for characterizing low-energy collective excitations in materials. RIXS is a powerful probe, which often requires sophisticated theoretical descriptions to interpret the data. In particular, the need for accurate theories describing the influence of electron-phonon ($e$-p) coupling on RIXS spectra is becoming timely, as instrument resolution improves and this energy regime is rapidly becoming accessible. To date, only rather exploratory theoretical work has been carried out for such problems. We begin to bridge this gap by proposing a versatile variational approximation for calculating RIXS spectra in weakly doped materials, for a variety of models with diverse $e$-p couplings. Here, we illustrate some of its potential by studying the role of electron mobility, which is completely neglected in the widely used local approximation based on Lang-Firsov theory. Assuming that the electron-phonon coupling is of the simplest, Holstein type, we discuss the regimes where the local approximation fails, and demonstrate that its improper use may grossly \textit{underestimate} the $e$-p coupling strength.

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