Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/17308
標題: La0.18Ca0.82(FeAs)2超導單晶熱擾動與上臨界磁場之研究
Thermal Fluctuation and Upper Critical Field of La0.18Ca0.82(FeAs)2 Superconducting Single Crystal.
作者: 邱欽浩
Ciou, Cin-Hao
關鍵字: 超導體
Superconductor
熱擾動
Thermal fluctuation
出版社: 奈米科學研究所
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摘要: 研究主要為熱擾動對超導單晶材料 Ca0.18La0.82(FeAs)2 傳輸特性的影響及探討其各向異性。我們用自我助熔劑的方法進行樣品燒結,可 以 穩 定 的 成 長 出Ca0.82La0.18(FeAs)2超導單晶材料,此 化 合 物 的 母 體 Ca(FeAs)2 為四方晶系的 Th(CrSi)2 結構 ,在正常態材料具有金屬性,電阻率與溫度關係成正比。 我們用La3+ 取代位於FeAs 層間的Ca+2,透過電荷轉移,增加了傳導層的載子濃度,並且使c 軸方向的晶格常數變長,結果引發了超導的特性。 超導相轉變溫度區間的寬度,隨著外加磁場及熱擾動所產生的磁導率而變寬,發現在不同的外加磁場下,透過適當的選取超導相轉變溫度Tc,會使得曲線收斂到同一條曲線上。進而經由尺度分析 ,獲得上臨界磁場Hc2。並且藉由估計得到的Hc2(0)推算出各向的超導相干長度ξab、ξc。另一項重要的發現,就是透過MPMS量測其磁滯曲線,得到此Ca0.18La0.82(FeAs)2 單晶超導材料的下臨界磁場Hc1 遠小於其它類型的超導體,約只有1高斯的數量級。
We have studied the thermal fluctuation effect on the transport properties of Ca0.18La0.82(FeAs)2 system. The single crystals of Ca1-xLax(FeAs)2 were grown by the FeAs self-flux method. The Ca(FeAs)2 has I4/mmm Th(CrSi)2 –type crystal structure. The resistivity shows metallic behavior in the normal state with the linear temperature dependence. As replacing Ca+2 by La3+ ion, the electron density increases in the FeAs layer via the charge transference, and the lattice constant of c-axis becomes longer. The results led to the superconductivity. The superconducting transition width broadened by the external magnetic field and the thermal fluctuation magnetoconductivity can be scaled by a universal function for all applied magnetic fields. The upper critical fields Hc2 are thus determined by the scaling analysis of the thermal fluctuation conductivity. The formula gives an excellent fit to the data. Based on the value of upper critical field Hc2(0), the superconducting coherence length is determined. We found that the lower critical field is abnormally small of 1 gauss.
URI: http://hdl.handle.net/11455/17308
其他識別: U0005-0208201316120000
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-0208201316120000
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