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研究生:黄瀚毅
研究生(外文):Han- Yi Huang
論文名稱:鐵基超導LaxCa1-xFeAs2超導特性的研究
論文名稱(外文):The superconducting properties of iron-based LaxCa1-xFeAs2
指導教授:藍明德
指導教授(外文):M. D. Lan
口試委員:李文新林彥甫
口試委員(外文):Wen-Hsin LeeY. F. Lin
口試日期:2016-07-13
學位類別:碩士
校院名稱:國立中興大學
系所名稱:物理學系所
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2016
畢業學年度:104
語文別:中文
論文頁數:53
中文關鍵詞:鐵基超導晶格常數釘扎效應自旋密度波
外文關鍵詞:iron-based superconductorLattice constantPinning effectSDW
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研究的材料為112-type鐵基材料中的LaxCa1-xFeAs2系列,目的是為瞭解三價鑭離子取代二價鈣離子後,影響自旋密度波的產生和超導特性。鐵基材料中的112-type跟122-type一樣,發生超導的關鍵在於FeAs層,間格層除了穩定材料結構還能提供載子。我們微量改變La跟Ca的摻雜比例,觀察樣品是否有超導及有無SDW產生,再進一步利用磁化強度的量測來觀察此系列的超導特性。
在實驗上,樣品使用固態反應法製作完後,利用XRD分析來了解其摻雜比例變化的晶格常數做比較。要了解此系列是否有超導特性,則利用MPMS來做分析,來得知樣品是否有出現完全反磁性,而在有超導訊號的樣品La0.18Ca0.82FeAs2和La0.2Ca0.8FeAs2之間,在同溫度下,電流密度Jc也有巨大的差異。利用四點量測得到的電阻對溫度圖,得知此系列在微小比例的摻雜下,就會影響SDW的產生。


We study the physical properties of iron-based 112-type pnictide superconductor LaxCa1-xFeAs2. The purpose of substituting Ca by La is to understand the correlation between Spin Destiny Wave (SDW) and superconductivity. Same as 122-type materials, FeAs layers are considered as an important ingredient for the superconductivity in the iron-based superconductors. The interval layers between the FeAs layers play as a role of carrier reservoirs. With the change of doping ratio of La and Ca, we observe superconducting behavior followed by the suppression of SDW.
The samples of LaxCa1-xFeAs2 is synthesized by solid state reaction with nominal ratio. The quality of the specimen is detected by the powder X-Ray diffractometer (XRD). The magnetic responses of superconductivity are further measured by the SQUID magnetometer. After comparing critical current density of La0.18Ca0.82FeAs2 and La0.2Ca0.82FeAs2 samples, we find that it has huge difference at 5K. DC transport behavior of specimen is measured by the standard four-point probing technique. The superconductivity is highly correlated to the occurrence of the SDW which is controlled by the doping composition of La.


摘要………………………………………………………………………………i
Abstract…………………………………………………………………………ii
目錄……………………………………………………………………………iii
圖目錄……………………………………………………………………………iv
表目錄……………………………………………………………………………vi
第一章 簡介………………………………………………………………………1
1-1超導歷史…………………………………………………………………1
1-2超導體特性………………………………………………………………3
1-3 鐵基超導…………………………………………………………………5
1-4 自旋密度波………………………………………………………………8
1-5單晶材料…………………………………………………………………11
第二章 儀器介紹……………………………………………………………………13
2-1 X光粉末繞射儀(XRD)……………………………………………………13
2-2 MPMS(Magnetic Property Measurement System)…………………………16
2-3 SEM (Scanning Electron Microscopy) ……………………………………18
2-4封閉式迴路冷卻系統 Closed Cycle………………………………………20
第三章 實驗步驟與方法…………………………………………………………22
3-1實驗流程圖………………………………………………………………22
3-2樣品配置………………………………………………………………23
第四章 實驗結果分析……………………………………………………………25
4-1 表面分析…………………………………………………………………25
4-2.1 X-ray結構分析………………………………………………………28
4-2.2 理論密度………………………………………………………………35
4-3.1磁化強度對溫度的量測………………………………………………36
4-3.2磁化強度對外加場的量測……………………………………………40
4-3.3 臨界電流密度…………………………………………………………45
4-4電性分析…………………………………………………………………49
結論…………………………………………………………………………………51
參考文獻……………………………………………………………………………52


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