磊晶碲化銻薄膜之成長與超導碲化銻/鈮多層膜之電磁傳輸特性之研究

Abstract

在本研究中，首先 Sb2Te3 靶材中加入額外之 Te 粉末，並以磁控濺鍍之方式製作Sb2Te3 薄膜，成功製作出 c 軸朝上之磊晶 Sb2Te3 薄膜，其 c 軸長度為 30.473 Å。之後製做 Sb2Te3 / Nb / Sb2Te3 三層薄膜與單層 Nb 薄膜進行磁性量測，在量測其磁化率時，觀察到在零磁冷時，三層薄膜會有明顯之順磁性效應，而在量測磁化強度與外加磁場關係圖時，在三層薄膜與單層薄膜接觀測到在下臨界磁場與上臨界磁場之間，若溫度遠小於 Tc 時，其曲線會有類似於震盪之現象，因此推論是渦漩生了改變，並引入順磁性邁斯納效應，成功解釋其機制。此外量測此兩樣品之磁滯曲線時，觀測到與一般超導體之磁滯曲線完全不同之現象，其磁滯曲線有兩個波峰，將磁滯曲線轉換成臨界電流密度時，發現兩樣品之臨界電流密度皆有先據烈增大而後衰減之現象，為解釋此現象引入 Second PeakEffect(SPE)，發現上下臨界磁場之間有一臨界磁場(Hg)，將渦漩分成固相及液相，在外加磁場接近上臨界磁場時，渦漩會經歷相變的過程，因此造成釘札力的增強，連帶影響了臨界電流密度與磁滯曲線，而本研究的數據與 Second PeakEffect 互相吻合，並製作此兩樣品之相圖。本研究也同時量測了微分電導，並比較了三層薄膜樣品、 Sb2Te3 / Nb 雙層薄膜樣品與 Sb2Te3 / NbSe2 樣品，分別量測在不同磁場與溫度下之超導能隙，並計算三種樣品在BCS理論下的超導能隙與Nb超導能隙之理論值來相互比較。

In this study, additional Te powder was added to the Sb2Te3 target, and an Sb2Te3 film was produced via magnetron sputtering. An epitaxial Sb2Te3 film with the c-axis oriented upward was successfully fabricated, with a c-axis length of 30.473 Å. Subsequently, Sb2Te3 / Nb / Sb2Te3 three-layer films and single-layer Nb films were prepared for magnetic measurements. The magnetic susceptibility measurements revealed a pronounced paramagnetic effect in the three-layer film at zero magnetic field cooling. When examining the relationship between magnetization intensity and external magnetic field, a phenomenon resembling oscillation was observed in the three-layer film between the lower and upper critical magnetic fields when the temperature was significantly below Tc. This behavior suggests changes in vortex dynamics and the introduction of the paramagnetic Meissner effect, which successfully explains its mechanism. Additionally, the hysteresis curves of these two samples exhibited a distinctly different pattern compared to those of conventional superconductors, displaying two peaks. When these hysteresis curves were converted into critical current densities, it was found that the critical current density initially increased and then decreased. This behavior can be explained by the Second Peak Effect (SPE). It was observed that there is a critical magnetic field (Hg) between the upper and lower critical magnetic fields, which separates the vortex into solid and liquid phases. As the external magnetic field approaches the upper critical magnetic field, the vortex undergoes a phase transition, leading to an increase in the pinning force, which in turn affects the critical current density and hysteresis curve. The data in this study align with the Second Peak Effect, and phase diagrams for the two samples were constructed. Furthermore, differential conductance measurements were performed on the three-layer film, Sb2Te3 / Nb bilayer films, and Sb2Te3 / NbSe2 samples. The superconducting energy gap was assessed under varying magnetic fields and temperatures, and the experimental results were compared with the theoretical superconducting energy gap for Nb according to BCS theory.