量子物質的光譜研究:(Ⅰ)硒化鐵、釔鋇銅鐵氧之超快動力學(Ⅱ)釔鋇銅氧共振類非彈性X光散射研究

Abstract

本論文我們以共振類非彈性X光散射研究超導體釔鋇銅氧薄膜的低能量激發，釔鋇銅氧薄膜由脈衝式雷射系統所製備，並且以熱處理系統進行後退火處理藉此得到不同電洞摻雜的樣品。比較不同入射光能量所量測之不同電洞摻雜能譜，結果顯示不同電洞摻雜下，電子在d軌域間的躍遷情形也有所不同。 此外，本論文中以飛秒雷射時間解析光譜的技術量測硒化鐵單晶，我們觀察到在結構轉變溫度90 K的前後，理論上硒化鐵結構對稱性由二重對稱轉變成四重對稱，然而我們亟欲想知道在轉變前後四重對稱的被破壞主要是來自甚麼機制的貢獻，因此我們作了一系列改變溫度和激發-探測光偏振角度的實驗，結果顯示電子nematic order的機制所造成的影響遠超過結構相變溫度90 K。 最後，本論文同樣以飛秒雷射時間解析光譜的技術量測釔鋇銅鐵氧，磁化率隨溫度變化的量測顯示在低溫175 K和高溫475 K分別都出現了反鐵磁的轉變，其中在TN1~175 K為Commensurate phase to Incommensurate phase轉變，我們作了一系列改變溫度量測瞬時反射率變化ΔR/R並進行分析，發現在Commensurate phase to Incommensurate phase過程中晶格與自旋熱平衡弛緩時間以及自旋重新排列時間有明顯的變化，並且在Incommensurate phase中，晶格與自旋之間交互作用隨著溫度下降也逐漸增強。

In this thesis, we studied the low energy excitation of superconductor YBa2Cu3O7-δ films by using resonant inelastic X-ray scattering. All the YBa2Cu3O7-δ thin films were grown by the PLD and the oxygen contents of YBa2Cu3O7-δ films were control with the annealing system. The results of energy dependence of RIXS show that the excitations of d electrons are different with various hole dopings. Besides, in this thesis we measured FeSe single crystals by pump-probe system. At the structure transformation temperature 90 K, the structure with two-fold symmetry transforms into four-fold symmetry. However we would like to understand what mechanism to change the symmetry. Therefore, the measurements in this study include two parts: the dependence of temperature and polarization angle of pump probe beams. The results indicate the mechanism of electron nematic order persisted up to 150 K. Finally, we measured YBaCuFeO5 single crystals by pump-probe system. Besides, a M-T curve indicates that the AFM transformations are emerged at low temperature 175 K and high temperature 475 K, which shows a commensurate to incommensurate magnetic structure phase transition at TN1~175 K. Therefore, we measured the transient reflectivity changes at various temperatures to study the relaxation behavior of photoexcited carriers. We observed that the spin-lattice thermalization time and spin reordering time change obviously at the transition between commensurate phase and incommensurate phase. In addition, the coupling strength between lattice and spin gradually increases with decreasing temperatures.