高溫超導體YBCO晶界約瑟芬接面的特性研究

Abstract

我們利用選擇性磊晶成長的方法在36°的鈦酸鍶(100)雙晶基板上製作不同微橋寬度的約瑟芬接面(Josephson Junction)，這些樣品的電流－電壓(Current－Voltage)特性和電阻分流模型(RSJ model)所描述的行為相近。此外在磁場效應方面，可以觀察到約瑟芬接面的臨界電流IC在磁場下的行為，IC隨著磁場強度作穩定的變化。即從整個圖形中可以看出超導電流繞射的效應。實驗結果亦發現在臨界溫度TC以下殘餘電阻的現象很明顯，樣品在一段不算小的溫度範圍內可以看到此現象，但是利用TAPS（Thermally activated phase slippage）理論實際去模擬，顯示此段溫區範圍內電阻－溫度的行為，並非TAPS的行為。這可能是因為在晶界接觸面上，非均勻性成份的接面所形成晶的結果。從I-V圖形中可以看出，正常態電阻RN對溫度的關係，可看出RN和溫度大致無關，而臨界電流與溫度的關係顯示這種接面的型態主要是屬於超導-絕緣-超導（SIS）接面的特性。

We use the process of selective epitaxial growth (SEG) to fabricate the〝Josephson Junction〞in forms of micro-bridges across the preformed grain boundary on a 36°SrTiO3 bicrystal substrate. These samples regardless of bridge linewidth, revealed current-voltage characteristics （IVC’s） that are well-described by the Resistively-Shunted Josephson Junction（RSJ） model. In addition, the critical current () of the junctions varies steadily with the magnitude of magnetic field, indicating the manifestation of supercurrent diffraction effect. However, the temperature dependence of the resistive transition though displayed residual transition, cannot be explained by the simple thermally activated phase slippage, commonly observed in weak-link junctions. This might originate from the spatial inhomogeneity at the interfaces. The IC(T) dependence, on the other hand, showed that these grain boundary junctions are behaving like Superconductor/Insulator/Superconductor (SIS) junctions.