釔鋇銅氧/鎳酸鑭雙層薄膜於鈦酸鍶(111)基板上之超導特性研究

Abstract

本研究以射頻磁控濺鍍製備釔鋇銅氧(YBa2Cu3O7₋δ, YBCO)單層薄膜與鎳酸鑭/釔鋇銅氧(LaNiO3/YBa2Cu3O7₋δ, LNO/YBCO)雙層薄膜。基板選用鈦酸鍶(SrTiO3, STO) (111)，並以YBCO作為底層建立異質結構。製備完成後，以X光繞射儀(XRD)與超導量子干涉儀(SQUID)進行結構與超導性質分析。 XRD 量測結果顯示，YBCO與LNO/YBCO薄膜皆可成功成長於STO (111) 基板上，且由繞射峰位置推得之YBCO (113) 面間距與文獻中塊材及生長於STO (100) 基板之YBCO薄膜存在差異，顯示薄膜之晶格參數可能受到成長條件或氧含量分佈之影響。儘管結構參數呈現差異，SQUID 量測仍確認所有樣品皆具有明確之超導轉變行為。 磁性量測結果顯示，所有樣品之Tc雖低於生長於STO (100) 基板之YBCO薄膜，但仍呈現清楚且穩定之超導轉變特徵。相較於過往STO (100) 基板上的樣品，本研究樣品之Hc1 (0)與Hc2 (0)皆隨Tc的降低而呈現一致性的下降趨勢。此外，由 M-H磁滯回線所推得之臨界電流密度Jc、釘扎力Fp的數量級顯示出與傳統YBCO薄膜不同的趨勢特徵。 在電性量測方面，雖然電性與磁性量測所得之絕對值存在差異，但整體樣品之變化趨勢高度一致。在Hc2-T/Tc關係中，STO (111) 基板上之樣品呈現與STO (100) 基板之YBCO薄膜不同的行為。此外，由ρ-T資料所萃取之釘扎能U/kB顯示，STO (111) 基板上樣品之U/kB相較於STO (100) 基板之樣品為低，且U/kB隨外加磁場增加而呈現近似線性下降的行為。此結果可由二維超導系統中之渦旋–反渦旋對解離機制加以理解，並可透過 Berezinskii–Kosterlitz–Thouless(BKT)特徵分析輔助判斷。

In this study, YBa2Cu3O7₋δ (YBCO) single-layer thin films and LaNiO3/YBa2Cu3O7₋δ (LNO/YBCO) bilayer thin films were fabricated by sputtering on SrTiO3 (STO) (111) substrates, with YBCO serving as the bottom layer. Structural and superconducting properties were characterized using X-ray diffraction (XRD) and Superconducting QUantum Interference Device (SQUID) measurements. XRD results confirm that both YBCO and LNO/YBCO films were successfully grown on STO (111). The interplanar spacing of the YBCO (113) orientation differs from that of bulk YBCO and YBCO films grown on STO (100), suggesting the influence of growth conditions or oxygen distribution. Despite these structural differences, all samples exhibit clear superconducting transitions. Magnetic measurements show that although the superconducting transition temperatures Tc are lower, stable superconducting behavior is maintained. The Hc1 (0) and Hc2 (0), decrease systematically with decreasing Tc, while the critical current density Jc and Fpexhibits behavior distinct from conventional YBCO thin films. Electrical transport measurements based on resistivity–temperature curves reveal consistent trends. In the Hc2-T/Tc, samples grown on STO (111) exhibit a scaling behavior distinct from that of YBCO thin films grown on STO (100). The activation energy U/kB is smaller for samples on STO (111) and decreases approximately linearly with magnetic field, consistent with quasi-two-dimensional vortex dynamics supported by Berezinskii–Kosterlitz–Thouless (BKT) analysis.