以共振軟X光非彈性散射研究氧化鎳,氧化鈷之電子激發態

Electronic Excitations of NiO and CoO Revealed by Resonant Inelastic Soft X-ray Scattering

黃筱妤(Hsiao-Yu Huang)

指導教授 ： 黃迪靖

國立清華大學/理學院/物理學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00468

摘要

強關聯電子系統的電子結構是凝態物理研究中一項重要的課題。許多新奇的物理現象決定於價電子間的強交互作用力，如高溫超導、龐磁阻等現象。其中過渡金屬氧化物在強關聯電子系統中扮演重要角色。對探測過渡金屬氧化物的電子激發態而言，共振軟X光非彈性散射是一個有效的實驗方法。藉由量測激發態的能量和動量轉移量的關係，可以提供系統的微觀電子結構。
在本論文中，我們使用新建的軟X光非彈性散射光束線，測量NiO和CoO的共振非彈性散射能譜。此實驗系統的建構是基於"能量補償原理"，即利用兩個相同且可調焦距的光柵作為單光儀和分光儀，可增加入射的光通量以補償微弱的非彈性散射訊號強度，且不影響能量解析度。在入射光能量為930 eV時，整個系統的能量解析度可達到240 meV。我們測量到dd excitations和charge transfer excitations的存在。藉由crystal field theory，可以完整解釋dd excitations並可得到crystal field的強度(10Dq)。此外，我們的實驗結果與SIAM理論計算一致。

關鍵字

共振軟X光非彈性散射 ； 過渡金屬氧化物 ； 強關聯電子系統

並列摘要

The electronic structure of strongly correlated electronic systems is an important issue in condensed matter physics, since the discovery of various interesting phenomena arising from strong correlations, such as superconductivity, colossal magnetoresistance, ...etc. Resonant inelastic X-ray scattering (RIXS) in the soft X-ray range is a powerful probe to investigate electronic excitations in solids. By measuring the excitation energies and the dependence of momentum transfer, the electronic structure can be further revealed.
In this thesis, we performed measurements of resonant inelastic soft X-ray scattering on NiO and CoO, by using a newly designed beamline based on an energy compensation principle. Two optically identical, actively bendable gratings were used as the monochromator and spectrometer. The RIXS spectra at L-edge with a combined energy resolution at 240 meV were obtained. We assigned different energy-loss features of electronic excitations from RIXS spectra to the dd excitations and charge-transfer excitations. The dd excitations are interpreted by the crystal field theory, and the crystal field strength (10Dq) is obtained. The RIXS spectra obtained with different incident photon energies are consistent well with the simulations by the single impurity Anderson model.

並列關鍵字

Resonant inelastic soft x-ray scattering ； Transition metal oxide ； Strongly correlated electronic system

參考文獻

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