論文摘要

從高溫超導體的發現至今，以鑭為基礎的銅氧化物在x~1/8 的特異現象始終是個令人費解的問題。近年來，stripe phase引起許多的注意，相關的實驗有中子繞射、拉曼與遠紅外光光譜、霍爾效應、熱電功率與磁化率等等。這些研究結果指出銅氧面上一維與二維間電荷轉移就發生在x~1/8 。
在本篇論文中，我們利用固態反應法合成了兩系列的p型超導體La2-xSrxCuO4與La1.4-xSrxNd0.6CuO4。大家都已經知道在兩系列樣品的
Tc - x相圖中，x~1/8 的地方會出現明顯的drop，而這個現象有可能與stripe phase有關。
這個有趣的問題促使我們利用X光吸收近邊緣結構光譜的實驗來研究電子結構的改變是否由stripe phase所造成的可能性。我們發現電洞載子的光譜權重是與摻雜量x有關而不是Tc。不過這些電荷stripes只在La1.4-xSrxNd0.6CuO4系列中觀察到，在La2-xSrxCuO4系列並沒有看到。我們的結果也暗示著La1.4-xSrxNd0.6CuO4系列中stripe phase的形成與結構相變無關，就像過去被大家相信的一樣。這些結果會與其他有關stripe phase的期刊論文加以比較。

Abstract

The x~ 1/8anomaly in the La-based cuprates had been puzzling since the discovery of high-Tc superconductors. Recently, the stripe phase which has attracted considerable attention in connection with many experiments, like neutron scattering, Raman and infrared(IR) spectra, Hall effect, thermoelectric power and magnetic susceptibility, etc. These results indicate that a crossover from one- to two-dimensional charge transfer accurs at x~1/8 .
In this thesis, we synthesize two series of p-type superconductors La2-xSrxCuO4 and La1.4-xSrxNd0.6CuO4 by solid-state reaction. It has been well known that there is a marked drop in Tc - x phase diagram at x~1/8 in both systems. It is possible that this phenomenon is related to the stripe phase.
This interesting question has motivated us to initiate the experiment of x-ray absorption near edge spectroscopy (XANES) to investigate the possibility of the electronic structure change caused by the stripe phase. It is found that the spectral weight of the hole carriers scales with the doping level x rather than with Tc . However, the charge stripe was observed in La1.4-xSrxNd0.6CuO4, but not in La2-xSrxCuO4. Our results also suggest that the formation of the stripe phase is not related to the structural phase transition in La1.4-xSrxNd0.6CuO4 consistent with earlier results. Comparisons are made between our results and those reported on the basic of the stripe phase scenario.

目 錄
page
圖目錄………………………………………………………..i
表目錄………………………………………………………..v
第一章 簡介……………………………………………... 1
第二章 基本理論
第一節 超導體的基本特性及現象…………………………8
第二節 超導體的電動力學…………………………………9
第三節 超導體的微觀理論………………………………..10
第四節 Stripe phase簡介…………………………………..15
第三章 基本實驗步驟
第一節 樣品的製程………………………………………..18
第二節 X-ray結構檢測…………………………………….20
第三節 電性測量…………………………………………..22
第四章 X光吸收近邊緣結構光譜
第一節 X光吸收光譜實驗的概念………………………...25
第二節 同步輻射實驗設備簡介…………………………..27
第三節 X光吸收近邊緣結構光譜的實驗流程…………..28
第四節 X光吸收近邊緣結構光譜的自我吸收效應之校正……………………………………………..33
第五章 測量結果的分析
第一節 樣品的結構分析…………………………………..38
第二節 樣品的電性分析…………………………………..39
第三節 X光吸收近邊緣結構光譜的自我吸收效應分析...42
第六章 結論……………………………………………..77
參考文獻……………………………………………………79

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