Sr3Cr2O8、CoO、Co(NO3)2與SrCuO2 之X光光譜線性二向性

Abstract

我們運用線性同步輻射光源研究Sr3Cr2O8, CoO, Co (NO3)2 與 SrCuO2等系統之軌道有序以及電子結構。在這篇論文中，Sr3Cr2O8 與CoO 這兩樣題目係由馬克思普朗克研究院，張春富博士之指導下完成。 在Sr3Cr2O8題目中，藉由線性偏振光研究單晶樣品的鉻L邊緣吸收光譜，我們可以得到鉻元素的電子組態、自旋二聚體的組成以及姜-泰勒效應(Jahn-Teller distoration)。藉由理論模擬，我們成功得出了Sr3Cr2O8基態波函數，軌道有序以及電子組態。 接著，我們同樣運用線性偏振光搭配理論模擬，對鈷的L邊緣吸收光譜進行深入研究。在鈷氧化物中，藉由氧化鈷成長於具延展性的雲母上，我們想探得基板應力對於薄膜之影響。然而，從結果來看，雲母與薄膜之間的交互作用僅有凡德瓦力。而在鈷氮化物中，硝酸鈷中的鈷離子擁有兩種不同的對稱結構，藉由理論模擬的協助，我們發現不論鈷離子的對稱結構為何，他們依然表現出總自旋數3/2的純高自旋態。 最後，我們將研究焦點放到鍶銅氧薄膜上(SrCuO2)，由於不同的經格結構是造成鍶銅氧系統是否為超導體的關鍵，因此，我們想得知薄膜厚度上的變化是如何改變晶格場結構。從我們的結果可以發現，如果薄膜的厚度小於10個單位經格的厚度，其結構係為鏈狀結構，反之則為片狀結構。而片狀結構在適當的參雜後即可成為超導系統。

We utilized synchrotron radiation linear polarized light to explore Sr3Cr2O8, CoO, Co (NO3)2 and SrCuO2 for its orbital ordering and electronic structure. In this thesis, Sr3Cr2O8 and CoO projects are supervised by Dr. Chun-fu Chang of Max Planck Institute, Dresden, Germany. For Sr3Cr2O8, we used linear polarized x-ray to measure the single-crystal sample for Cr L-edge absorption spectra to explore the chromium electronic structure and spin dimers formation, and Jahn - Teller Distortion. Along with the multiplet theory, we find the ground state wave functions, orbital ordering, as well as the electronic structure for Sr3Cr2O8. We also study cobalt oxide and cobalt nitrate using linear polarized light of Co L-edge x-ray absorption spectroscopy and deploy theoretical calculations in order to analyze the spectra. In the case of cobalt oxide, we use extendable substrate MICA in order to investigate the effect of the strain influence on the thin films. However, from the results, it seems that the mechanism for CoO growth on MICA is only related to Van deel war force. In the Co(NO3)2, cobalt ions have two different sites, which is divided by the way they are distorted. Assisted by the theoretical calculations, we find out that even the cobalt ions are in different local structure, they still show a total spin of 3 / 2 as the purely high-spin state. In addition, we also focus on SrCuO2. We want to investigate how the thickness of SrCuO2 influences the crystal field. It is an essential element for shaping superconductivity. Our result indicates that if the thickness is thinner than 10 unit cells, it grows in chain-like structure; while above 10 unit cells, it become plane-like structure leading to superconductivity with appropriate doping.