Nb/Sb2Te3多層薄膜中磁通釘札行為與渦旋動力學之研究

Abstract

本論文研究不同堆疊配置之Nb/Sb2Te3多層薄膜的磁通釘札行為與渦旋動力學，並建立一套規範化且具再現性的分析架構，由溫度與磁場相依的磁化量測中取得超導轉變溫度、特徵磁場、臨界電流密度 J_{c} 與釘札力密度 F_{p}。磁性響應呈現多重超導轉變特徵，顯示此多層薄膜無法以單一均勻的超導態描述。透過分析 J_{c}\left(H\right)、F_{p}\left(H\right)、歸一化釘札力與對數 J_{c}\left(H\right)，可辨識出不同的釘札區域與類第二峰值行為，顯示渦旋響應會隨磁場及溫度演變。

最值得注意的是，當磁場平行於 ab 平面時，系統於約3 K呈現異常的低場釘札增強。排除受額外磁性訊號影響的區域後，面外方向並未重現相同的增強現象。此方向差異顯示該異常增強具有異向性，且對多層膜介面敏感，而非僅源自傳統的塊材Nb釘札。儘管僅憑磁性量測尚無法唯一判定其微觀來源，本研究結果仍為進一步探討Nb/Sb2Te3多層薄膜中受介面調控的渦旋動力學提供了實驗基礎。

This thesis investigates flux pinning behavior and vortex dynamics in Nb/Sb2Te3 multilayer thin films with different multilayer configurations. A standardized and reproducible framework was established to extract superconducting transition temperatures, characteristic magnetic fields, critical current density J_{c}, and pinning-force density F_{p} from temperature- and field-dependent magnetization measurements. The magnetic responses exhibit multiple superconducting-transition features, indicating that the multilayer films cannot be described by a single homogeneous superconducting state. Analyses of J_{c}\left(H\right), F_{p}\left(H\right), normalized pinning force, and logarithmic J_{c}\left(H\right) reveal distinct pinning regimes and second-peak-like behavior, demonstrating the evolution of the vortex response with magnetic field and temperature.

Most notably, an anomalous low-field pinning enhancement appears near 3 K when the magnetic field is applied parallel to the ab plane. No comparable enhancement is reproduced in the out-of-plane configuration after excluding regions affected by additional magnetic signals. This directional contrast indicates that the anomalous enhancement is anisotropic and sensitive to the multilayer interfaces, rather than arising solely from conventional bulk Nb pinning. Although its microscopic origin cannot be uniquely determined from magnetic measurements alone, these results provide an experimental basis for investigating interface-modified vortex dynamics in Nb/Sb2Te3 multilayer thin films.