三碲化二銻/硒化鈮和金/硒化鈮異質結構的超導性能

Abstract

本研究主要探討了拓撲絕緣體Sb2Te3以及金屬Au與二維材料NbSe2形成的異質結構的超導特性。實驗由台科大透過化學氣相傳輸（CVT）方法生長出的NbSe2單晶，經過加壓退火處理後，將20 nm的Sb2Te3和Au分別鍍在NbSe2上，形成不同的異質結構。這些結構的電子性質通過電阻率測量和磁阻實驗進行了詳細的分析。研究發現，Sb2Te3/NbSe2顯示了明顯的超導轉變，而Au/NbSe2則作為參考系統展示了與Sb2Te3/NbSe2相比較的性質。此外，我們觀察了Sb2Te3/NbSe2結構中的釘扎效應和BKT相變行為，這些發現對於理解異質結構中的超導機制和超導態的微觀物理行為具有重要意義。 從電阻率對溫度的測量我們發現Sb2Te3/NbSe2的Tc為7.04 K略高於Au/NbSe2的6.88 K，前者平行於樣品表面的磁場的上臨界溫度Hc2為14.73 T則是高於後者的9.11 T，表示著典型的導體可能有著破壞Ising 超導的效果，而垂直於樣品表面的磁場的Hc2前者則大幅上升至8.88 T，後者則小幅的下降至5.75 T，使得兩樣品的各向異性都大幅下降。接下來利用V-H圖分析釘扎力，發現前者的釘扎力在兩個方向上都比較大，意味著能夠承受更多的臨界電流。再來由V-I圖的斜率得到α與溫度的關係，以此來得出BKT相變溫度TBKT，也比較了加磁場前後的差別，觀察到兩個樣品的TBKT均有下降，證明了其二維的性質。最後利用從小電流量測出磁場平行表面的Hc3再與理論值的Hc3 = 1.695 Hc2做對比，可以發現典型的金屬鍍層會使表面超導存在的空間更大。

This study primarily investigates the superconducting properties of heterostructures formed by the topological insulator Sb₂Te₃ and the metal Au with the two-dimensional material NbSe₂. The NbSe₂ single crystals were grown at NTUST using the chemical vapor transport (CVT) method, and after annealing under pressure, Sb₂Te₃ and Au were respectively deposited on NbSe₂ to form different heterostructures. The electronic properties of these structures were thoroughly analyzed through resistivity measurements, and magnetoresistance experiments. The study found that Sb₂Te₃/NbSe₂ exhibited a significant superconducting transition, while Au/NbSe₂ served as a reference system, showing comparative properties to Sb₂Te₃/NbSe₂. Additionally, we observed pinning effects and BKT transition behavior in the Sb₂Te₃/NbSe₂ structure, which are crucial for understanding the superconducting mechanisms and microscopic physical behavior in heterostructures. From the resistivity vs. temperature measurements, we found that the critical temperature (Tc) of Sb₂Te₃/NbSe₂ is 7.04 K, slightly higher than the 6.88 K of Au/NbSe₂. The upper critical field (Hc2) parallel to the sample surface for Sb₂Te₃/NbSe₂ is 14.73 T, higher than the 9.11 T for Au/NbSe₂, indicating that typical conductors may have a detrimental effect on Ising superconductivity. When the magnetic field is perpendicular to the sample surface, the Hc2 for Sb₂Te₃/NbSe₂ increases significantly to 8.88 T, whereas for Au/NbSe₂ it slightly decreases to 5.75 T, greatly reducing the anisotropy of both samples. Next, by analyzing the pinning force through V-H plots, we found that the pinning force in Sb₂Te₃/NbSe₂ is larger in both directions, meaning it can withstand higher critical currents. Furthermore, from the slope of the V-I plots, we obtained the relationship between the exponent α and temperature, and thus determined the BKT transition temperature (TBKT). We also compared the differences before and after applying the magnetic field, observing a decrease in TBKT for both samples, confirming their two-dimensional nature. Finally, by measuring the upper critical field Hc3 and comparing it with Hc2 in the direction parallel to the sample surface, we found that the typical metal coating allows for a larger space for surface superconductivity. These findings provide valuable insights into the design and optimization of new quantum materials and devices.