摻雜稀土元素對鐵基超導RE0.18Ca0.82(Fe0.92Co0.08As)2 的影響

鐵砷族化合物層是鐵基超導體中很重要的一部分，物理學家認為超導性就是來自這裡，上下層的化合物的功能只是為中間的鐵砷層提供電子或由此取出電子，另外反鐵磁的漲落很可能在超導電子配對過程中扮演不可或缺的角色，對母體中的長程反鐵磁序壓制，常常會讓超導電性顯現出來，所以我們推測摻雜了稀土元素後，所造成的晶格結構的變化，可能會間接的抑制長程磁序的產生。 本實驗主要是探討摻雜稀土元素對 RE0.18Ca0.82(Fe0.92Co0.08As)2 的影響，當摻雜稀土元素時會改變材料的晶格常數，而晶格常數正是影響超導特性形成的原因之一，於是我們利用 XRD 分析儀來對其摻雜後的晶格常數做比較，並且利用 Closed Cycle Refrigerator Systems 量測出其電性，是否有產生超導電性，另外磁性部分則是利用 MPMS 來做分析，可以得知是否有完全抗磁性，接著我們發現晶格常數的改變對於超導臨界溫度，有一個奇特的趨勢，另外我們也證明了稀土元素的大小並不影響超導特性，而是摻雜後所改變的晶格常數才是主要影響因素。Magnetism and superconductivity(SC) are two outstanding quantum phenomena, and the relationship between the magnetic and superconducting orders has naturally become an important subject in condensed matter physics. So we focus on iron-based superconductors. In general belief that the superconductivity is highly correlated to the FeAs layer in the iron-based superconductors. Other layer compounds only offer electronic for intermediate layer. Antiferromagnetic fluctuations are likely to play an integral role in the superconducting pairing process. The parent of the long-range antiferromagnetic ordering repression, superconductivity will often show up. So we speculate that the rare-earth-doped after the elements, caused by changes in the lattice structure may indirectly inhibit the generation of long-range magnetic order. This experiment was to investigate the effects of doping on RE0.18Ca0.82(Fe0.92Co0.08As)2. When the rare earth doped materials will change the lattice constant which is the impact of the formation of the superconducting properties one of the reasons. So we use XRD analyzer to compare its lattice constant after doping and the use of Closed Cycle Refrigerator Systems measure its electrical resistance. The other part is the use of magnetic MPMS do the analysis, we can know whether there is totally anit-magnetic. And we can change the lattice length number generated for the superconducting properties for it or not, to do a detailed comparison.第一章超導簡介…………01 1-1 超導歷史…………01 1-2 超導特性…………04 1-3 鐵基超導…………06 1-4 自旋密度波(Spin Density Wave) …………08 第二章儀器介紹…………10 2-1 X-ray 粉末繞射檥(X-ray diffraction) …………10 2-2 變溫電阻量測系統(10K close cycle…………13 2-3 超導量子干涉儀(SQUID) …………15 第三章實驗步驟與方法…………16 3-1 樣品製備…………16 第四章實驗結果與數據分析…………21 4-1 X-ray 分析…………21 4-2 電性量測…………27 4-3 磁性量測…………32 4-4 數據分析…………36 第五章結論…………41 參考資料…………4