本論文的目的是在探討第二類超導鈮薄膜線在大電流驅動後平衡的磁通
量子渦流形成結構。探討此渦流的形成和分佈不僅對闡明外加電流超越臨界電流後的崩潰機制有重要的意義，還能對實際應用面的極限能有更多理解。我們使用外部磁場、電流和溫度等變量研究鈮薄膜線中渦流之形態，並通過使用自製的掃描超導量子干涉儀顯微鏡(Scanning Superconducting Quantum Interference Device Microscope, SSQM)觀察。

本論文的內容主要包括兩部分，第一部分，我們會詳述本文使用的SSQM
系統。為了提升SSQM 之效能及簡化其製備過程，我們改進了初始系統設計。主要的改進包括集成了本實驗室先前所定制的掃描式霍爾探針顯微鏡(Scanning Hall Probe Microscope, SHPM)所使用的掃描方案、新的懸臂設計和低溫LC共振電路設計，其技術細節我們詳載於附錄中。

第二部分為主要的量測結果與討論。鈮薄膜線樣品是以直流濺鍍系統濺鍍鈮金屬，再利用圖案化技術將鈮薄膜處理成蜿蜒形式的幾何形狀而成。特別地，樣品中我們另外設計薄膜線來外加磁場以局部操縱渦流。我們採用所謂的電流加熱程序瞬時驅動超導線進入正常狀態，觀察到渦流往往形成在無序之區域，這些渦流通常是可移動的，並且可以通過使用交互磁場和發送高電流而在中心區域中減少並傾向於在圖案邊界附近積聚。我們的結果表明薄膜質量和幾何形狀對超導薄膜線的應用的重要性。

This thesis aims to investigate the configurations of equilibrium vortices formed in superconducting niobium (Nb)-thin film wire after high current drive. The formation and distribution of vortices in superconducting thin film have strong implications not only for elucidating its breakdown mechanism as the external current applied exceeds the critical current density, but also for understanding its limit in practical applications. The vortex morphology of thin-film wire is studied with the variables of external magnetic fields, currents and temperatures and is observed by using a home-made Scanning Superconducting Quantum Interference Device microscope (SSQM).

The content of this thesis is comprised by two parts. In the first part, we will describe our SSQM system. To enhance the capability of SSQM and to simplify its operation, we improve our original design. The primary improvements include the integration of the scanning scheme used in our custom-made scanning Hall Probe microscope, new cantilever design, and the low temperature tank-circuit design. We leave extensive technical details in the Appendixes.

The main results and discussions are presented in the second part. The sample made by Nb thin-film is prepared by DC sputtering and is patterned into a zigzag geometry. In particular, we employ in-suite thin-film wires to introduce magnetic field to locally manipulate the vortex. We adopt a current heating procedure to transiently drive the superconducting wire into the normal state. We observe that the vortices tend to form in the disordered regime. These vortices are in general movable, and can be depopulated in the central area and tend to accumulated near the pattern boarders, by using alternating magnetic field and sending high currents. Our results suggest the importance of thin-film quality and the geometry for the applications of superconducting thin-film wires

目錄

摘要 1
Abstract 2
致謝 3
目錄 4

第一章 超導體現象與磁通量子渦旋之介紹
1.1 超導歷史簡述 6
1.2 超導理論與第二類超導體中磁通量子旋渦 7
1.3 磁通量子渦流文獻回顧 16
1.4 實驗動機 19
1.5 磁通研究工具-磁性顯微鏡系統之簡述 20

第二章 掃描式超導量子干涉顯微鏡(Scanning Superconducting Quantum Interference Device Microscope) (SSQM)
2.1 DC-SQUID理論 28
2.2 SSQM結構之概觀 37
2.3 空間掃描方式 40
2.4 低溫系統設計 41
2.5 SSQM電系設計 42
2.6 SQUID載台 44
2.7 SSQM雜訊分析 47

第三章 實驗樣品
3.1 DC-SQUID製程與設計值 51
3.2 DC-SQUID特性量測 55
3.3 鈮薄膜超導蜿蜒線樣品之設計 59
3.4 鈮薄膜超導蜿蜒線樣品之特性量測 62

第四章 實驗結果與討論
4.1 外加磁場驅動磁通量子渦旋 64
4.2 超導相變過程後磁通量子磁通渦旋形成與分佈 71
4.3 交互強磁場變換驅動磁通量子渦旋 78
4.4 不同厚度之鈮薄膜磁通量子磁通渦旋討論 83
4.5 結論 89

第五章 總結與未來展望 90

參考文獻 91

附錄一 SQUID控制器操作 93
附錄二 三軸步進馬達控制器配置與設定 110
附錄三 SSQM系統冷卻程序 114
附錄四 LC諧振電路(tank circuit) 119
附錄五 樣品貼近SQUID感測器之訊號 122
附錄六 SQUID載台工程圖 128

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